As I'm writing this, I just got back from the grocery store. I had a 5% off coupon good for my entire purchase (with some exceptions, of course). The coupon was set to expire on 12/25, and I wasn't sure when I would have time to do a serious shop before then, so when the free time came up, I decided to start a grocery list.
While 5% off isn't a whole lot, I wanted to get as much use out of it as possible without using it as an excuse to buy things that I normally wouldn't buy. Instead, I decided to use this as a chance to stock up on a few things, items that wouldn't expire and that would definitely get used. I made a list and hit the store. Surprisingly, the one time I'm going with a plan to spend money is the one time that I just barely cross $100. I stocked up on frozen goods, soup, cereal, and cat litter, among other things. Nothing too exciting. I just wanted to be sure that I didn't splurge on any other items, and I think that's how I kept the bill low.
So while I saved about $10 with the 5% coupon and other coupons, I think I inadvertently taught myself a lesson about being careful about what I put into my shopping cart when I hit the store.