At one of the hardware stores, each time I would do the shop (every 3 months), I would get one of those little flashlights by the checkout counter. I have four kids. Each kid got one. It's great for when they have to get up and go to the bathroom at night or get scared or something. I also got one for myself to keep in my purse. It's come in so handy.
At fashion stores, I usually buy a pair of earrings if there is nothing that I want or need at the moment. I can always give them as gifts or pass them to my daughter, in her stocking or something.
At one store, I got the little silver things by the register. Those things that have nice and inspirational sayings on them...I put them at the kids' breakfast spot from time to time; or tuck them under their pillows while they sleep when they've had a hard day.
For the gas station/convenience shops, I will often buy the quart sized milk. It goes over by a few cents, but my kids go through a gallon of milk a day, so to get four gas station shops in one day, while ferrying them hither and yon, gives me a day's worth of milk for them...I usually do the shops on the way home from wherever, or take a cooler bag with me
I can only get milk, though, if I do them all in one day, and I don't get milk every time (I'm afraid always buying milk would blow my cover). So when I do them on different days, each kid gets to pick out a treat, on a rotation. We just remember who got theirs last time....We also use this method when we travel/go on vacation and I pick up gas station or convenience store shops.
One day, my kids were heading to a field trip with some other homeschool kids, and we were out of bread, so I didn't make them lunch. I did the gas station shops on the way to drop them off and got each of them "lunch stuff..." sandwiches, jerky, package of cookies to share, apples and bananas, a salad bowl... we always have a case of water in our car (always for games, practices), and so they just took the shop stuff and a bottle of water and were good for the day....