Here´s a small geometric tool which will not only fit into every pencil case, but also in every small pocket - a trapezoid ruler. Without any numbers on it, you can still draw straight lines, as well as a 45 degree, a 60 degree, a 120 degree and a 135 degree angle. Print it with transparent filament and you will still be able to see the drawn lines on the paper when holding the ruler onto it.
I'm a student who found his fascination for 3D Printing when our school got a 3D Printer. Furthermore I'm interested in modeling things with a CAD software. Have fun while browsing through my things!
If you have special wishes for things I could design, please let me know! :D