Duct Tape

The single best invention since sex. It can be used to mend or repair almost anything. Fixing torn bags, packs and tents. Stops your handlebar tape from unravelling. Torn into long strips, it makes an excellent emergency rim strip. It's durable waterproof, and fiercly adhesive.If you can't fix it with this, maybe it can't be fixed!

Denim patches

That's right, the same ones mommy used to use to save your favorite blue jeans can also save your tires. They are light weight, reusable and tough as, well, blue jeans!
Use the 2" x 3" size for road tires, the 4" x 4" for fatter dirt stompers. slip them in between the tube and the damaged tire casing. Use duct tape if you're having trouble holding them in place. They can be bought at just about any supermarket at about ten for just over a buck.

(Note: I've found out from friends, that the 2" x 3" patches are not good for tears much larger than 1/2" in length.)

35mm Film cans

These can be obtained at any camera store that does film finishing, if you don't use it yourself. They are great for storing small items. I have four in my carry on first aid kit. For sunscreen, Ben-Gay, antiseptic, and medicines.

In my tool box at home they hold ball bearings, small nuts and screws, etc.

When touring they come in handy for holding grease and other things that "may" be needed when something goes wrong fifty miles from nowhere.

I prefer the ones made for Fuji film. They are clear, so you can see what's inside. And the lid fits tighter.