When stocking up, do bear shelf life in mind. Canned meats, for example, last quite a long time, but spices don't last long at all. So if you go to Costco and see a gigantic container of ground cinnamon, think twice. It's unlikely you'll be able to use all that cinnamon before the flavor dissipates.
There are a few rules of thumb you can follow. Whole spices last longer than ground spices, for example, and flours and grains kept in air-tight containers last longer than those kept in their original bags. (To extend their life even longer, place whole, dried basil leaves every few inches inside the flour or grain to keep moisture and bugs away.)
What you buy for your pantry depends entirely upon your family's tastes. Here are some things I like to have in my pantry, but feel entirely free to omit and add to this list as you see fit:
Canned and dried beans
Family favorites (like boxes of macaroni and cheese, cereals, breakfast bars, coffee, etc.)
It's likely you'll waste money if you don't organize your pantry in a way that makes it easy to rotate foods. The easiest way to do this is simply to place the most newly-purchased items toward the back of the pantry and move older items forward as you do so. Can dispensing racks, which automatically move older cans forward, help tremendously with this.
At least once a year (and preferably twice a year - perhaps during spring and fall cleaning) remove everything from the pantry and clean the shelves. Replace the contact paper, if necessary, and if there's a way to make the pantry more attractive, better organized, or easier to use, take the time to implement it.
Read Part I of the Plentiful Pantry series