I cannot draw or cut things straight. Ever. My bulletin boards are famed for their wonkiness. So before I began teaching I invested in a small paper guillotine. The sharp bit is hidden inside so I can't chop off my thumb but just watch it make short work of card sorts or halving worksheets.
I simply can't explain how time-saving this device is and how much students respect the straight lines it provides. Even if your school resources room has a big one, I still suggest getting your own. You will use it more than you can imagine.