giftcards

say you have 2 giftcards for the same place, but with different amounts.  use up the one with less money first so you'll sooner end up having to tote around just one card.  then when you get home, use a sharpie to write the new amount that's left on the card.  that way you're not left thinking, "dude, i could have sworn there were twenty more dollars on this card."