We recently made a long trip to visit family, and one of the first things I did was visit a nearby military base to purchase some basic, over-the-counter medical supplies at the Exchange. My mom questioned this, and I explained my logic:
We are a family of six, with four busy kids. Not a day goes by that someone doesn't need some ibuprofen, or some hydrocortisone, or (especially when traveling) some allergy medication, and we seem to be sick more when traveling. I've seen the prices for these medications in the real world, and they're scary! At the Exchange, I can purchase all the ingredients for a very basic first aid kit for less than $10. For $20, I can purchase nearly everything we could imagine needing. If I'm not prepared, it is nearly inevitable that I'll be making a late-night search for a 24 hour pharmacy, driving some distance (and usually to a sketchy area) to overpay for something simple. Sometimes, we might not need all of the things we've purchased, and that's OK. We're prepared, and we usually save money, too.
The same strategy works for other items. If you are able to anticipate certain needs, and take advantage of the things that are excellent prices at certain stores (military Exchange or not), you can save a bundle by a little anticipatory shopping. It is almost a no-brainer to stock up on school supplies during the summer sale season, when you can get notebook paper for 10 cents a pack and colored pencils for a quarter. It makes me crazy when I have to pay full price for office supplies because I need something mid-year. And I love that the dollar stores sell poster board for 50 cents - much better than the prices elsewhere, and I would much rather head for my little stash than be out scrounging poster board for last-minute needs. (Tip: I slide mine behind a bookshelf, my friend uses magnetic clips to keep it on the side of her refrigerator.)
I'd love to hear if you have developed a good system for taking advantage of the great prices available at certain stores or during certain times of the year. I can always learn more, and I'm sure some other readers will benefit, as well.