Haha, so true! I do this at the grocery store too. Always reaches a point of wanting nothing more than to get to the checkout and get the heck out of there! (Bonus points for making it there without dropping anything or having your fingers go numb, lol.) It's especially handy at the big warehouse stores, because you can navigate a LOT faster w/o a cart.
(Besides, being focused on the carrying discourages browsing.)

Also agree with "if you don't have it, you can't spend it". Another thing I do is not look! That was a big help getting Ebay under control. Oh yeah.

Edited to add: And not having a credit card. Can't possibly spend what I don't have.