One way that I am able to keep from overspending is to collect all my change and save it specifically for going to garage sales. Then, I gather it in a plastic bag, and once it's gone, well it's gone!
I had saved up a Zip-Loc bag full of change, and it lasted a full week on my visit to Kansas City, where I spent a little less than $15. Here's a portion of it that set me back $3.75. Yes, that's a piece of J & G Meakin ironstone underneath the Missouri plate.
Always Frugal, Always Fabulous
The Elegant Thrifter