Never Forget Who Borrows Your Stuff Again!
This is easily one of the best life hacks I've ever found and since finding it a couple months ago, I've put it to use several times and laughed every time I've had to go back and find the proof.
I recently photographed my father with my Passport before a trip to London because he really likes to be in control of my travel accessories even at the age of 30. The next morning when he questioned whether I gave it to him, I pulled out my iPhone and BOOM!
If I had learned this one in college, I'd know exactly who had all my sweatpants, sweatshirts, xbox games, money and maybe even all those keg shells.