Always carry dental floss, says Annie Getchell, the author of The Essential Outdoor Gear Manual (McGraw-Hill). Getchell is something of a backcountry Mary Poppins: She totes a small, magical bag filled with oddments—from electrical tape to hose clamps—that can see her through any mishap.

Floss comes in handiest, especially for sewing together thick materials such as the neoprene of wet suits, the leather of hiking boots, and the nylon of backpacks.