Junk

Junk. This supposedly useless item is actually one of the most useful items in the game... in the right quantities.

I'm sure you noticed the 'discard junk' option while talking to Wayne. If, during the course of your adventure, you give Wayne 300 pieces of Junk, he'll use his MacGyver-like technical aptitude to turn all that worthless crap into one of the game's ultimate guns. You can either have him create a specific type of gun, or you can leave him to his own devices and have him create something for you at random.

There are not many places in the game where you can get Junk; in fact, only four enemies have a chance of dropping it. First, there's the birds found in Central Park and floors two through ten of the Chrysler Building. These birds are your best bet, since they have a high chance of dropping it and appear in packs. The frogs in Chinatown's sewers can drop Junk, but they don't drop it often enough, nor do they appear often enough, to make it worthwhile. It's the same with the lizards in the Museum. Finally, Chrysler Building slimes found on floors sixty-one and up drop Junk just as often as birds do, but they're much tougher.