Granted, my pantry is a little bigger than most, however the rule of thumb is the same: have enough ingredients to pull a meal together at a moment's notice- hence, Spaghetti alla Puttanesca (literally "spaghetti a la whore" in Italian) which is a tangy pasta dish invented in the mid-20th century by women who would put a simple pasta dish together for their gentleman callers. The ingredients are typical of Southern Italian cuisine: tomatoes, olive oil, olives, capers and garlic.
I like to organize the pantry according to items that are used together such as baking items, dried spices, condiments, canned items, cereals, etc. Why is it important to organize the pantry? It saves you money by identifying what you're using and not using, allows you to take stock of your cooking habits, and tells you what you should and should not buy in bulk. Need help getting started? Real Simple magazine has provided a checklist which you can print out which includes the essential items you should have on hand in both your pantry and your refrigerator: http://www.realsimple.com/food-recipes/shopping-storing/food/pantry-staples-checklist-00000000000197/