Replacing a gear cable — don't leave home without one

Spare chain link. Be positive that it fits your chain, and that of your riding partner.

Baling wire. Pack about ten inches of this lightweight, inexpensive, available-at-hardware-stores wire. It's just the thing for temporary repair if something big breaks. Something big on the bike, that is — not on you.

Duct tape. Carry a very small roll of this (a few feet will do) for temporary repair if something small breaks, or if your riding partner is talking too much (sometimes just the threat works). It can also be used as a tire boot if nothing better is present.

Rear derailleur pulley. No, I've never lost one. But I've never worried about losing one since I popped one in my tool bag. I did so after talking to two hard-riding, hard-repairing bike shop mechanic friends in Utah.

Spare nuts and bolts. Especially rack-mounting bolts.

Lubricant. There is a host of great little bottles of lubes to choose from. And any of them is better than none when a chain link starts squeaking or a cable or derailleur freezes up.

Spare gear and brake cables. One each, just in case. Nothing lasts forever. At least nothing mechanical.