I have used my save-a-dive kits many times- fin straps, mask straps, o rings, mouthpiece, reg and hose changes. And almost every time it is for someone else. Of course the rule of "you can use it, but if mine breaks, I get it back" applies. I have o-rings, ties, wrenches, screwdrivers, picks, mask and fin straps, snorkel holder, lube, bungies, aquaseal, mouthpiece, pencils, chapstick, tank light, etc. All fits in a 6 inch x 4 x 4 Otter box- tightly. I also have a smaller second one for my camera equipment with ll the requires specialized items. Lastly, I usually have a couple of extra hoses, and if going somewhere somewhat remote, a second reg set.
Just last night in the pool helping a class, had to change out a regulator for one of the students and replace my tank o-ring.
I have been made fun of several times- on a boat in Curacao, a bunch of my friends started razzing me about it, calling me anal. On that day and the next day, a fin strap and a mask strap broke for other divers. Funny, they stopped teasing me....
Terry
PS- I also carry a 2 foot piece of 3/16" poly rope tucked into a corner of my BC pocket. Only pulled it out once- my buddy, at depth, had clip issues with a fin and it wouldn't stay clipped. Tied off the rope around the clips on each side and around the heel, and while not pretty, we completed the dive.