Since baking POWDER will go bad in time, it is easier/better to store the ingredients in your prep supplies.
Since Baking Powder is made using Creme of Tartar, which is derived from wine making, it is probably
not going to be easy to make by "hand". So stock up now. You can always plan on making your own wine,
but you will need access to grapes...
The process of making Baking Powder is described in this short article;
http://modernsurvivalblog.com/survival-kitchen/how-to-make-your-own-homemade-baking-powder-and-why/#more-42626If you plan on using this for cooking, do include a copy of these instructions in your Prepper Recipe docs.
The basic mix is 2 parts Creme of Tartar, 1 part Baking Soda
Add 1 part Corn Starch if your making a larger batch for storage.
The Corn Starch is NOT needed if you making only enough for the immediate recipe usage.