Split Screen way for unlimited keys: Xbox Live
Player one's profile needs to be on the harddrive. ( This person will be grabbing all the guns )
Player two's profile should be on a USB drive.
Clear your system cache and disconnect from Xbox Live. ( The update prevents this glitch )
Load in, ( Prefferable you should laready both be saved in sanctuary next to the gold chest )
Have Player two open the chest, and player one pick up guns. ( Do this twice if you have the Shift key too )
Unplug the usb ( Where player two has his account saved. )
Now when you save it'll save both characters to the hard drive, BUT player two's save that still has both the keys is saved on the USB. ( Which was unscathed because you removed it. )
Now plug back in the usb, ( Important: Not only does player two have to reslect the USB as his storage device, but he also has to hit (Y) and select his character again. )
If player two does not reselect his character, he will load in with the hard drive save, even if the usb was selected.
Once you believe you have enough guns to split them up evenly, do so. ( I do this with my buddy split-screen because we can trust one-another )