What's the big deal about keeping the wallet slim? Like a lot of good grooming/menswear habits, it's all about the neatness of your overall presentation. A bulging George Costanza-style wallet is hurting your image every time you stick it in your pocket: A thick wallet makes an asymmetrical bulge under your clothes. It looks like some sort of tumor. Not stylish. A heavy wallet in one jacket pocket makes the whole thing sit slightly lopsided. Your shoulders will look uneven and a little hunched. Using the same thick wallet day in and day out will eventually create faded creases in whatever pocket you use, in the shape of the wallet, shortening your clothes' lifespans. If it's really overfilled you look bad when you pull it out, too. There should never be fringes of tattered paper or badly-bent plastic cards sticking out when you produce your wallet in public. So before we get into what a man shouldbe carrying in his wallet, let's be clear: he shouldn't be carrying anything that isn't regularly needed and vital to have on the person at all times.