An officially-licensed Bioshock “Big Daddy” backpack from Thinkgeek:

This backpack features a flap with the porthole design from the helmet of Bioshock’s iconic Big Daddy. The portholes are a mixture of yellow, red, and green so nobody will know what your next move is likely to be. Gotta keep ’em guessing. And it comes with your very own Little Sister plush charm. Better protect that.

[Bioshock “Big Daddy” Backpack]