I carry around a pipe caliper that I designed and 3D printed. A scissor-looking device that tells you the size of a pipe (up to 4") based on outside diameter. Useful on the job.
I designed and printed a custom flashlight holder for those cheap LED flashlights.
Custom replacement handle for a triangular file
Set of custom drawer knobs.
Custom hard drive mounting bracket.
Custom battery holder.
Custom shelf bracket.
~Three dozen clothespins.
3-axis tilt camera stand that mounts on top of a tripod. (replaces one that broke).
Custom 80:1 worm gear reduction for a machine I was working on, as well as a few spur gears and light-duty V-belt pulleys for same machine. Custom thrust bearing and ball bearing holders.
A full set of Meta-Chess pieces.
A custom tool for aligning V-belt pulleys using a 3V line laser module and magnetic base.
Currently in progress is a mostly 3D printed racing wheel controller for my PC, which uses the guts from a dual analog game controller. The controller is unusable because the silicone pads for the buttons cracked, but the electronics are still good and with 4x analog axes I can get steering and three pedals plus 16 digital buttons. My hangup is I can't get the "feel" of the buttons right...
If I ever get off my ass and finish building the electric furnace I've been working on, and manage to melt some aluminum with it, I fully intend to try lost-PLA casting some aluminum parts. That's be awesome...