I wanted to make my own Swiss Army style keychain.
This 2nd version is quite a bit smaller than the first one I did. I added my own take on the swiss army logo.
Use 3 3mm socket cap screws (length depends on how many keys you want to use) and nuts (sized for 3mm nylocks), assorted washers.
Using washers will make the keys easier to pull out and get a decent snugness. But you could lose them if you wanted a smaller overall thickness.