If you need to weigh something small but don't have an appropriate scale on hand, Redditor Pedipalp has a MacGyver-worthy solution that turns a simple clothes hanger into a balance scale.
Pedipalp needed to weigh a package before he shipped it to see if he could send it in a mailbox, but he didn't have a scale at home. So he measured out 475mL of water in a Ziploc bag, taped it and the package to a hanger, and discovered that it was, in fact, safe to put in the mailbox. It isn't going to give you super-accurate results, but when all you need is an approximation, this is a genius little tip that you can put together in just a few seconds. Hit the link for more details.