I find it hard to resist impulse buys for myself when I'm out shopping or running errands. So I go ahead and scoop things up - and put them in a box when I get home. The box contains a variety of things at different price points. When I've earned a reward for meeting a goal, I choose something from the box. It's as good as going shopping all over again - and gives me something to look forward to.
This works great for stuff I find on sale (shoes!) or little things like bookmarks and stationery. I also find it very motivating because I really want the stuff that's in the box, but can't get to it unless I ear n it.