I really am only just starting to even think about this,
Here is my Long winded wish list of stuff I'd like to buy reasonable priced :
Cool looking costume maybe starting with the helmet.
Camera rigs for more then a GOPRO .. seriously gopro are spoilt and every other camera make is just neglected.
(while we are at it lets do some cool camera stuff ... like a- barn doors and filter hood , focus rail holders , tripod mount for simple crane design , or perhaps some tripod mounts that are designed to hold more then a gopro...maybe even a flash bracket that holds a flash and a softbox mount for a flash to make it nice and diffused)
Armatures for stop motion .. yes it still happens that despite being rather good in 3d I rather like doing stop.
3d prints that would work as assembly parts -for things like interaction with sprinkler piper fittings to make more parts that are super light weight and work in combination of more cheap readily available units to allow creation of many things (especially quick to fabricate temporary shelters for things that need cover) Eg : lookup pvc pipe glasshouse... now imagine if you didn't need glue or special tools to assemble one.. you could dismantle it and take it with you (good for renters)
Car Parts : More models and more awesome sauce .. example custom door trims for cars , door buttons for older classics , Tyre tube caps that are custom looking (example a skull or a bird ect ) Seat Belt holder , air vents for certain models that no longer supply them , Window cranks for old cars that are difficult to find , Custom interior light covers
Custom Glove Box compartments .. this would be difficult to make but imagine the show off value it.
Cake : I actually had a request from someone to make a cake tier model ... sadly I didn't have a 3d printer and had to advise him to continue on in his search for custom cake tiers...
Really am wanting to get myself a 3d printer soon.