I was lucky and use to live down the street from a antiques "mall" that had hundreds of stalls with all sorts of stuff (might work if you're near a flea market?) and occasionally I'd take $10 only with me and find "The" item :-) I've done it in grocery stores (limit how much you take with you and find the one item that you most "want") and I imagine it could be done in a dollar store.

As a matter of fact, I made a collage of "chores" and numbered them, rolled dice and had to "do" whatever number chore I rolled. One of the numbers was for the dollar store; I had to go to the store and buy a single item and then bring it home and use it. It got my creativity going :-) and made doing chores fun.

Think of a literal project to do and get the items at the dollar store or go see if you can find the most out-of-date food item in the dollar store and buy it :-) I've bought batteries there, not looking at expiration date and they were a several years out of date, LOL.