What is/was your most creative/helpful use of 550 cord?

I just made a clothesline this weekend for the sheets, and my better half made me a cake as a result.

550cord=cake

very helpful!

Watching movies on Kindle downrange..

OK, don't laugh, but here it is... I'm pretty sure your 550 cord is akin to our aviation 'tie-string' that is often used to secure wire bundles for aircraft.
Its a small, waxed nylon string that can be used in all sorts of things... and believe me, it has been.
Its been used by us, for pinata hanging, securing tent flaps, tieing down things in the back of a pickup during moves, making drying lines when the dryer broke, and in one memorable instance, using it to control the accelerator on my Jeep when the dang linkage broke during a trip... yes, picture it, annoyed mother driving while screaming children are TOUCHING each other in the back seat, using a piece of tie-cord fed thru the fire wall and dash as an accelerator, finally understanding why there were times when my mother would want to sit in a corner and just scream her head off.
On a further note, I got the linkage repaired the next day, but I still have nightmares about that trip!