A dead cell phone battery. It can happen to anyone. And the only known cure is keeping a spare power cord handy everywhere, at all times. This keychain DIY project has to be the easiest and cutest way to do it.
Aki of Minted Strawberry made this cord wrap as gifts for friends with just leather, a key ring and a well-placed snap. There is a bit of light sewing involved, but it's nothing a novice with a needle and thread can't handle.
The strip of leather (or felt, or any other material) is sewn down to create snug loops that grip onto a plug or coiled cord. Measurements for where to cut and sew will be specific to whatever is going into the key chain cord wrap, but Aki's post on Minted Strawberry has details and measurements for a basic USB-cord coil like what's shown here.
More info and Minted Strawberry
If the three letters D, I, and Y just aren't part of your vocabulary, there's a retail solution, the $17.99 Scosche flipSYNC II, which looks like a typical car alarm dongle, but unfurls into a handy USB 2.0 cable connector (note, a Lightning edition is currently unavailable).
(Images: Minted Strawberry)