He is about the say that banks don't buy "items" when I unlock the box and pull out a tray of gleaming gems. Soon the whole bank staff is around the table (we're standing at one of those tables the bank has for customers to finish signing their paperwork), and I am handing around items. The gem tray is set aside, and I start handing ancient artifacts to the floor manager. Some are from ancient Rome, Greece, and as I dig deeper into the box the artifacts get more modern. Then I start taking out artifacts from the future. "Here's the bank 5 years from now", and 50, and 100. Everyone is impressed and interested, and it is obvious the bank is going to buy the lot.
Also, everyone takes it for granted that everything in the box is genuine, and nobody even thinks to ask how I got things from the future. I have no idea either, I just have these things, as a collector who is selling his collection. I don't think I'm a time traveler, or know anyone who is.