Great topic!

Broken zipper on tent door. Sewed and safety-pinned that door shut, then used the door on the other side for the rest of the trip.

My wife's pack tore open at the bottom. The problem was that there wasn't quite enough material in the seam. We re-sewed it with dental floss...and it has now carried us hundreds of miles,

Water filter plugged. Yeah--this one was on a spring hike with very high, muddy water. And we didn't have a backup filter. We melted snow in our pots and bottles by putting them in a black bag and leaving that in the sun.

Scariest of all: Almost ran out of matches! We each thought the other had packed them...and we ended up with ten matches for five days. And we made every single one of them count!