Putting a Limit to How Much Kids Buy

The kids seem to think that everytime they go to any store or garage sale they have to buy something. They used the excuse that it was their own money they were spending, but a $2 allowance can only go so far and I wanted them to learn to save some of it. Even though I tried to explain to them why it wasn't a good idea to have to find something to buy just because they walked in a store, they just weren't getting it. So, finally, I started a One In, One Out Rule. It really works, if they know they have to get rid of one of their things they aren't so quick to buy something!