I hate wasting food, but at the same time, don't want to ruin a dish or baked good with an ingredient that isn't fresh (or worse, rancid!)  Some things have expiration dates, but for the most part, I rely on my senses, which is not necessarily a good judge either!  Here's a site that really breaks it down: http://www.pastrywiz.com/storage/index.html.  I'm not sure about some of it.  For example, I have an unopened bag of whole wheat flour sitting in my pantry (well over a month).  Who knew I should have been refrigerating it?  I think maybe I'll still rely on touch and the 'ole sniffer some, but when I'm really stuck, this is a good guide.