Put your favourite 3D print model into suspended animation inside a sealed glass chamber.
Just mount (glue) your model onto the base and screw it into the jar.
Use it as a key chain or as an ornament.

I picked up these really cheap glass scintillation vials at Active Surplus (Queen St., Toronto). I wanted to use them as miniature display cases so this 3D model is a screw on cap for the vials.
The screw was designed specifically for this particular vial so I don't know what else it might fit.

There are three versions of the cap with varying heights depending on how tall your model is. Each version comes with or without a hole for a keyring so there are actually 6 variants altogether in this thing.