One of my favorite subreddits is /r/functionalprint, where users showcase 3D prints that are useful. Here are some of my functional prints:

Tripod Handle

Printed in TPU (soft and rubbery). The original had disintegrated.

Coffee Spoon Holder

Created early on as a simple, and sort-of funny, test. It turned out to be quite useful.

Tripod Shoe with Ball Attachment Point

Useful for phone cameras and similar. Required a few iterations to strengthen ball mount post enough to stop breaking every time I dropped it. Switching to PETG helped.

Hitec 5055 Servo Mounts

Mini servos can be difficult to mount. This one is being used for Hitec-5055MG servos on TankRobot-FPV

Bicycle Post Holders

PPE Head Bands

Visor headbands for Personal Protective Equipment shields intended for emergency medical staff, first responders, and similar. NIH approved model by 3DVerkstan. My impressive neighbor, Michael K. Johnson, was the organizer for our area. He handled assembly and shipping of everything I sent him, in addition to doing a serious amount of his own printing using his customized 3D printer(s).