If you pack smart and light, you can get away with one diaper bag for twins. It's easy to think that you'll need twice the stuff, but remember that many things can be shared. You will need more bottles and more diapers and more pacifiers and maybe an extra outfit, but wipes, the changing pad, burp cloths, toys, and even blankets can be shared. As long as the diaper bag you choose is either large capacity or designed specifically for twins, there's no need to double up on diaper bags. Save that money for better things! You won't have enough arms to carry that extra bag, anyways.