One of the things you need to figure out to coupon effectively is how much of a product to buy when you hit a deal at a rockbottom price. The idea is you buy enough to last until the next sale cycle. It's called stockpiling, which always brings the show "Hoarders" to my mind, but if you do it right you will have enough to last until it goes on sale again, but not TOO much.
As you shop the sales you will start to notice a pattern. Most items go on sale at least once in a 6-12 week period, and as you tune into that, you'll be able to make better choices about how much to buy. Some items hit thier best price seasonally (think chocolate chips and other baking items during the holidays, or barbecue sauce and ketchup in the summer).If you know you'll use these things and you have the space to store them properly you can stock up more than you might use in 12 weeks for these types of items.
Which brings me to my point about expiration dates. I read this article in Slate which confirms what I already believe. Expiration Dates, Sell by dates, best by dates, etc. are pretty conservative. I'm not suggesting you ignore them completely, just that you use your best judgement before throwing things out based on a date on a package. Obviously the more perishable an item the more careful you should be, but if it has been stored properly, it looks and smells fine, it's probably ok even if it is past the date.