The following was discovered at: http://www.survival-center.com/foodfaq/index.htm?

Baking Powder
This powder is a combination of an acid, an alkali, and a starch to keep the other ingredients stable and dry. The powder reacts with liquid by foaming and the resulting bubbles can aerate and raise dough. Almost all baking powder now on the market is double acting, meaning it has one acid that bubbles at room temperature and another acid which only reacts at oven temperatures. Unless a recipe specifies otherwise, this is the type to use.

Don't expose baking powder to steam, humid air, wet spoons, or any other moisture. Store in a tightly lidded container for no more than a year. Even bone dry baking powder eventually loses its potency. To test its strength, measure 1 tsp powder into 1/3 cup hot water. The mixture should fizz and bubble furiously. If it doesn't, throw the baking powder out.

For those folks concerned with aluminum in the diet, the Rumford brand has none in it and there may be others.

Baking Soda

This gritty powder is sodium bicarbonate also called sodium acid bicarbonate (NaHCO3), a mild alkali. It is used in baking to leaven bread and does so in the same manner as baking powder. When combined with an acid ingredient, the bicarbonate reacts to give off carbon dioxide bubbles which causes the baked good to rise. If kept well sealed in an air- and moisture-proof container its storage life is indefinite. If kept in the cardboard box it usually comes in, it will keep for about eighteen months. Do keep in mind that baking soda is a wonderful odor absorber. If you don't want your baked goods tasting of whatever smells it absorbed then keeping it in an airtight container is an excellent idea.

Herbs and Spices

It is difficult to give exact instructions on how best to store culinary herbs and spices because there are dozens of different seeds, leaves, roots, barks, etc., we call an herb or a spice. There are, however, some general rules to be followed to best preserve their flavors. All spices, particularly dried, are especially sensitive to heat, air and light. Room temperature is fine for keeping them and refrigeration or freezing is even better, but they should be kept away from heat sources. It is common for the household spice cabinet or shelf to be located over the stove, but this is really a very poor place. Dark opaque glass is best for storage, but failing that, keeping a tightly sealed glass container in a dark place is next best. The cellophane packets some products come in just won't do for storage. Tightly sealed metal containers will work as well. Even dense plastic will do, but glass is best.

Where possible, buy spices whole. Whole nutmegs will keep their flavor far longer than ground nutmeg, the same for other seeds and roots. You'll have to use a grater, grinder or whatever, but the difference in flavor will be worth it.

If you buy spices in bulk containers (which is certainly cheaper) consider transferring some into smaller containers and keeping the larger one tightly sealed in a cool, dark place. This will prevent unwanted light and air from continually getting in and playing havoc.

Included in the suppliers addresses are listings for several spice and herb companies. The one I have personally dealt with so far is Penzey's and their products have been consistently good. It's worth investigating some of these companies as they can really take the sting out of purchasing large quantities.

Salt
 Storage life for salt is indefinite. So long as you do not let it get contaminated with dirt or whatever, it will never go bad. Over time, iodized salt may turn yellow, but this is harmless and may still be used. Salt is rather hygroscopic and will adsorb moisture from the air if not sealed in an air-tight container. If it does adsorb moisture and cakes up, it can be dried in the oven and then broken up with no harm done.

All salt, however, is not the same. Salt comes in a number of different varieties, each with its own purpose. Very little of the salt produced in the U.S. is intended for use in food. The rest of it, about 98%, has other uses. Therefore, it is important to be certain the salt you have is intended for human consumption. Once you are satisfied it is, you should then determine its appropriateness for the tasks to which you might want to set it to. Below is a partial list of some of the available salts. I hope to make it more complete as I find better information.

Table Salt
This is by far the most widely known type of salt. It comes in two varieties; iodized and non-iodized. There is an ingredient added to it to absorb moisture so it will stay free flowing in damp weather. This non-caking agent does not dissolve in water and can cause cloudiness in whatever solution it is used if sufficiently large quantities are used. In canning it won't cause a problem since there is very little per jar. For pickling, though, it would be noticeable. If you are storing salt for this purpose, you should be sure to choose plain pickling salt, or other food grade pure salt such as kosher salt. In the iodized varieties, the iodine can cause discoloration or darkening of pickled foods so be certain not to use it for that purpose.

Canning Salt
This is pure salt and nothing, but salt. It can usually be found in the canning supplies section of most stores. This is the salt to be preferred for most food preservation or storage uses. It is generally about the same grain size as table salt.

Sea Salt
This type of salt comes in about as many different varieties as coffee and from about as many different places around the world. The "gourmet" versions can be rather expensive. In general, the types sold in grocery stores, natural food markets and gourmet shops have been purified enough to use in food. It's not suitable for food preservation, though, because the mineral content it contains (other than the sodium chloride) may cause discoloration of the food.

Rock or Ice Cream Salt
This type of salt comes in large chunky crystals and is intended primarily for use in home ice cream churns to lower the temperature of the ice filled water in which the churn sits. It's also sometimes used in icing down beer kegs or watermelons. It is used in food preservation by some, but none of the brands I have been able to find label it as food grade nor specifically mention its use in foods so I would not use it for this purpose.

Solar Salt
This is also sometimes confusingly called "sea salt". It is not, however, the same thing as the sea salt found in food stores. Most importantly, it is not food grade. It's main purpose is for use in water softeners. The reason it is called "solar" and sometimes "sea salt" is that it is produced by evaporation of sea water in large ponds in various arid areas of the world. This salt type is not purified and still contains the desiccated remains of whatever aquatic life might have been trapped in it. Those organic remains might react with the proteins in the foods you are attempting to preserve and cause it to spoil.

Halite
For those of us fortunate enough to live in areas warm enough not need it, halite is the salt that is used on roads to melt snow and ice. It, too, is not food grade and should not be used in food preservation. This form of salt is also frequently called rock salt, like the rock salt above, but neither are suitable for food use.

Salt Substitutes
These are various other kinds of metal salts such as potassium chloride used to substitute for the ordinary sodium chloride salt we are familiar with. They have their uses, but should not be used in foods undergoing a heated preservation processing, as they can cause the product to taste bad. Even the heat from normal cooking is sometimes sufficient to cause this.

Yeast
Yeast is just not a product you can stow away and forget about until you need it next year. It is, after all, a living organism and if it's not alive at the time you need it, you won't get any use out of it. This ancient leavening, brewing, fermenting agent is a single celled microscopic fungus. When we incorporate it into our bread dough, beer wort or fruit juice it begins to reproduce madly (we hope) and produce several by-products. If you're baking, the by-product you want is carbon dioxide which is trapped by the dough and subsequently causes it to rise. In brewing or vintning what is wanted is the ethyl alcohol and, if the drink is to be carbonated, the carbon dioxide.

Almost all yeasts used for these purposes are in the same genus (Saccharomyces or "sugar fungi"), but several different species have evolved and some are more suitable for a particular task than others. It's entirely possible to use grocery store bread yeast to brew beer or ferment wine, but the results may leave a great deal to be desired. It's also possible to use yeast from beer brewing to make bread and from what I've read the results were pretty much indistinguishable from bread yeast.

Leaving aside the brewing and vintning yeasts which are really outside the scope of this FAQ I am going to concentrate on bread yeast. It comes in two generally available forms; compressed or fresh and dried, sometimes called granular or instant active dry yeast. They are different genetic strains of the same species, but have different characteristics.

Compressed yeast is only partly dried (about 70% moisture) and requires refrigeration and keeps even better in the deep freeze. If kept in an air- and moisture-tight container to prevent it from desiccating this type of yeast will keep for a year in the freezer (0 degs F or less, but only about two weeks (maybe a bit more) in the refrigerator. Unless your kitchen is rather chilly it will not keep on the shelf. It should not have a mottled color or a sour odor.

Dried yeast has only an 8% moisture content and comes packed in foil envelopes. The smaller single use packets are not generally vacuum packed, but the larger commercial sized "bricks" of about a pound or two each generally are. They can last for months on the shelf, up till the expiration date which should be clearly stamped on the package. If packaged in the same manner as recommended for compressed yeast above and kept in the refrigerator or freezer it can last for several years. The larger packs of yeast should be transferred to an air and moisture tight container after opening.

Either type of yeast can be tested for viability by "proofing" it. This is nothing more than mixing a small amount of the yeast with an equal amount of sugar in warm water (105-115 deg F for dried; 95 deg F for fresh). Within about five minutes active yeast will become bubbly and begin to expand (at normal room temperature). Yeast which only slowly becomes active can still be used, but you will have to use more of it. If it shows no activity at all, it's dead and should be thrown out.

There is another means of providing yeast for baking besides buying it from the grocery store and that is by using a sourdough starter. I'm not going to address it here, but I will point out that it has a newsgroup all its own (rec.food.sourdough) and several FAQ's devoted to it. Drop in and read for awhile and you'll learn more than you thought you could ever want to know.