There's an entire industry dedicated to squeezing as many tiny tools as possible onto the keyring you carry every day. But the usefulness of miniature scissors or a petite pair of pliers can't compare to the sheer number of repairs you can make with 18-inches of duct tape in your pocket.
Roughly the same size as a tube of lip balm, this keychain-friendly roll of duct tape can actually hold anywhere from 18 to 61cm of duct or gaffer tape, depending on its thickness. For $US20 ($27) you get your choice of brass or stainless steel finishes, plus a matching keyring.
When your emergency supply of duct tape runs out, the empty spindle is actually easy to refill if you have access to an electric drill. You just attach the spindle to the chuck like a drill bit, secure the loose end of your duct tape roll to it, and start it spinning at its lowest speed. In seconds you'll once again be prepared for any emergency -- from something as big as your bumper falling off, to something as small as an unexpected clothing tear.