a cool 'gadget' for your wallet
Rummaging around in the links on Jason's blog, I found a reference to this thing called a wallet buddy.
Basically, it's a little envelope (you print their PDF out on paper, cut it out, fold it, and glue it together) sized just right for your debit card or credit card.
Then when you pull out your plastic to buy something, the list will remind you to think again about whether you need to spend the money.
You could use this to hold gift cards, too, and then just write the amount that's left (though the folks at Barnes&Noble do that right on your card w/ a Sharpie)