Check out this post from the Jodie and Julie at Food Storage Made Easy. If you aren't familiar with their website, this is a good time to check it out. This is one of the best websites out their for those new to the food storage scene.
Baking powder is a real must for baking, and yet its storage life is quite short. Store the basic ingredients, baking soda and cream of tartar (both of which have very long storage lives) and you are set for years of baking to come.
Another great site is Safely Gathered In, which recently posted on this same topic.