How many times has this versatile material come in handy for you? To many to count most likely, so let's hear about the time when it really saved your hide, or just came in really handy.
I was working overseas awhile back and my team was in an operations room with alot going on. Somebody tripped on a phone line and it broke where it had been pinched by a computer desk. The only tool I had on hand was my SAK and three or so feet of duct tape is keep in my wallet wrapped around an old ID card. So I proceeded to splice the phone cord back together and used the duct tape as an insulator. We returned later to repair it properly. But it worked well enough temporarily for everyone to keep working.
It may not be my wildest fix or use for it but it was probably the most important.