IKEA BAGGEBRO feet
I have a BAGGEBRO shelf that stands on a uneven carpet that is causing it to lean over a bit.
This simple 3D print rises the front two legs by 6 mm, solving my issue.
I can also imagine this being useful as anti-skid feet.
PLA
999 walls (perimeters), this gives it high strenght and load capacity, and it barely costs more filament or time than any combination of walls/infill.