Most handy prints I have done so far are axis alignment tool and belt tension gauges to help make setting the belt tension on the K1 easier and correct.
Sounds like there are a lot of “engineers” here but I’m not so my “useful” things may pale in comparison but they work for me! All are my personal designs. I just have fun designing practical things. I’m not a “trinket” person.
Sponge holder
Comb (hair)
Bed scraper
90° Corner cable/headphone holder
Custom GoPro Hero 3 Panoramic Adapter for 360 shooting
Custom Nikon EnEl3 and GoPro battery magazines
Custom Cut sheet alignment guide for my Epson 7900
Phone/Tablet Holders
Other cool things for my business
I just started printing last month so I haven’t had a lot of “alone time” to design more useful things (which is why I purchased a 3D printer)
I’ll probably look into mods for my Phantom 2 this summer.