Ask HN: What would you 3D print if you had a printer?

On Saturday I'm picking up a 3D printer I just bought. I've got some ideas for things to make and some models I've made over the years but I'm curious what other people would use it for if they had one. My flatmates and workmates fancy guns but I don't have my firearms license yet so I'm holding off on that front.

And if you do have one, what do you use it for?