Update it with USB so that it can take input and return results. Hook it up to a cash register for something like an antique store. Ideally one selling small items so that the customer can marvel at the display adding things up.
I also have always wanted one of those mechanical vintage cash registers, for the same reason I have always wanted a Curta. They always seemed like they would be fun to play with.
I could probably get one of those cash registers to play with for not a ton of money, but my house isn't huge and it's hard to justify the space.
