#1 - A small, "cute" tabletop garbage can.
With 3D printing, you will have little bits of extruded plastic EVERYWHERE. My middle school students were notorious for leaving scraps laying around, or brushing them onto the floor. Enter one "cute" garbage can. Now they can't wait to put their scraps in there, and they even like looking inside of it to see their collection of scraps and failed prints grow. (I can't explain them, I just teach them.) :) It's also easily portable, and we move it around the room as different tools and 3D printers fall in and out of favor with the group. I bought this one at Target.
#2 - A 3D print display stand (ie: a non-slip spice rack)
the spice rack. Still room for improvement, but it's better. I plan to order a second one. Of course you can build your own, but I (embarrassingly) was looking for a cheap, immediate, injection-molded solution.