A simple thing to help people get back on thier feet after a full loot, which is probably what most people put money in the bank for anyways. Just a few restrictions would keep it from eliminating the regearing aspect of the game, if that should be preserved at all(IMO, it shouldn't, but still...). It could be a really small, no bigger than a large sack perhaps. If it was really nessicary to keep people from keeping a set of gear in it, there could be a limit of no items greater than half of the character's lvl in the box. And of course, like most containers, no limited items aloud. With such restrictions, it would mainly be used to store food and water, and maybe some simple potions or some basic weapons, perfect for a start after a death/full loot.

I doubt it would be that hard to implement either. It could work something like you pay 100cp and the teller gives you the box. then it works just like a regular container, and you do 'deposit box' when you've got everything you need in it. Then to get it again, jut 'withdraw box'.