Be prepared to foil pick-pockets with a decoy wallet. Having anything stolen from you is saddening - unless you make something specifically designed to be stolen! Note that this is not for use if you are being robbed!
Step 1: Supplies
You need some sort of a wallet. The one I have pictured was a gift from my brother and I honestly would be sad about losing it. I'll make a replacement decoy or keep an eye out for a cheap one to use.
A singing card. This isn't critical but sure does make the project more fun and the decoy much more enjoyable to show friends.
Business cards, expired gift cards, or other junk to thicken up the wallet.
Anything else you would like to stuff in there to further prank the thief. I used some relevant cards from a game of Apples to Apples, some cards from a deck, and a page from my daily bacon calendar.
You may also need scissors, glue, a translation book, and a pen.
Step 2: Some money
Of course, this step is completely optional. You might not want to give the thief any money at all! Pictured is one USD which is of almost no use in the places I usually travel (bills must be over $20 and totally crisp in order to be exchanged), 23 cents worth of Chinese currency, and about 20 cents worth of Mongolian currency. It is just the right mixture that the recipient will surely know that the wallet was intended to be lifted.
Step 3: Filler
I added some playing cards, business cards (some of use to me but duplicates of ones that I really need), and relevant cards from Apples to Apples that describe the wallet. Having the wallet thick enough to be noticed is important. You want the thief to focus on it instead of your bag, your friend's thinner wallet, or the bills and cards you have tucked elsewhere. This thing should look like the mother-lode!