Q: Which plants in the U.S. can be used as emergency water sources?

If you're stranded, say, in the desert, with a sweltering sun above and no water in sight, plants—even those covered with thorns—may start to look mouthwatering. But lopping off the top of a barrel cactus with a machete and sucking on the white flesh inside is not the answer to your thirst.

"Tapping a cactus like a water faucet is a myth," says outdoor education instructor and photojournalist John Annerino (see "National Park War Zone" in the February issue—read excerpt), who resorted to hacking out the foul pulp just once over the course of trekking 10,000-plus miles [16,000-plus kilometers] of the Sonoran Desert. An hour of work produced one gulp of juice—which he promptly spit out.

Better to save your sweat and use former U.S. Air Force survival instructor Paul Green's advice: Cover a tree branch or the stems of a bush with a clear plastic bag. Cinch, and within eight hours you should have at least a pint of condensation—even with slim pickings in the flora department.

"I tied a transpiration bag on a tree in Corpus Christi that looked like it'd been nuked," says Green. "It collected a cup [0.24 liter] in a half hour."

If you really want to drink water straight from the stem, you're limited to wild grapevines, found in woodlands throughout the U.S. "Cut out a good middle section of the plant," says Eustace Conway, a modern-day Daniel Boone and the subject of Elizabeth Gilbert's The Last American Man, "and it will just drip, drip, drip into your mouth." Draw more water-divining tips from Wilderness Survival (Stackpole Books).

Q: How can I pack light for a two-day ride on Moab's White Rim Trail?

Alas, the quickened tempo of modern life! The hundred-mile [160-kilometer] classic of Utah mountain biking (see White Rim Trail photos) is usually covered in three to four days by outfitters, giving riders time to absorb their Canyonlands surroundings while the gear follows in a 4x4. (At the other extreme, diehards ride the whole thing in a day.)

Freeskiing champion and White Rim fan Alison Gannett—who's ridden the trail in one, two, three, and four days—advises you to check the weather report and then leave your tent and stove at home if you'll be out only overnight.

She straps a sleeping bag and a pad to a rear rack, then stuffs clothes, energy bars, and tools into her biggest hydration pack. She also carries a water filter, enabling her to refill from the muddy Green River. Any more than two days, though, and she arranges for a 4x4.