I bought a 50-pack of plastic centrifuge tubes for $(removed) on Amazon a couple of years ago. I was planning to use them to do geocaching with my daughter but we both lost interest. I left the tubes in a bag in the garage.
A couple of weeks ago I needed a screw to fix something. I have a plastic bin filled with loose hardware – nuts, nails, screws, picture hangers, wire nuts, and so on. When I reached in, I poked my finger with a thumbtack. It wasn't the first time that a sharp thing in the box had poked me, so I decided to sort the stuff into separate containers. As I thought about what kind of containers I should use, I remembered the centrifuge tubes. I used those.
I could have just kept the tubes in the same plastic bin that I'd used to hold the loose hardware, but since I have a new Original Prusa I3 MK2S 3D printer (which is amazing), I went ahead and made a wall-mountable tube holder. I used Tinkercad to design it. Here's the model.
I used double sided foam tape to mount the tube holder on the wall. I'll need to print out 10 of these to hold all 50 tubes.