(From the archives, this post deserves more reader contributions! Can’t believe I missed duct tape, added at the end.)
Fire Starter

Fire starter made from petroleum jelly and dryer lint.
Why it rocks: Add a few shavings from your fire starter stick, strike a spark, and you’ll ignite anything but floating driftwood.
Paper Towels

They work, but pack out what you pack in.
Why they rock: A classic multiple purpose item, unlike toilet paper will continue to function when moist. Also doubles as fire starter when twisted up with wax or PU ski strap shavings.
CPR Mask

CPR mask
Why it rocks: Save your buddy’s life.
Sunscreen

We couldn't face publishing an ugly sunscreen shot. Use your imagination. You've been there.
Why it rocks: Because melanoma is worse than imaginary face fungus.
Custom Footbeds
Why they’re ugly: Anything your feet stood on for ten hours a day would eventually be defined as the last word in grossness.
Why they rock: They prevent blisters, make you ski better — and some chiropractors claim they even cure rabies.
Energy Gel

Energy gel might take the prize. Even so, we like the stuff.
Why it rocks: The stuff works like rocket fuel. Use it and big days are yours. We prefer the GU brand variety, but it all works to one degree or another. Main thing is to test and see what agrees with your stomach. Beware of caffeine versions if you limit your buzz bean intake.
Old Skins (that still rock, and carry small rocks.)

Yuck. Old climbing skin glue.
Why they rock: You made them that way, because you did so many laps your skins finally gave up. And they include rocks.
Duct Tape
Dean shared the details in his comment:
Why it is ugly: “It’s always wrapped haphazardly around something else essential. And by the time you make it home, it’s peeling a bit in an attempt to imitate your old skins.”
Why they rock: “Because of the age old tool box rule: if it moves and it’s not supposed to…”
WildSnow.com publisher emeritus and founder Lou (Louis Dawson) has a 50+ years career in climbing, backcountry skiing and ski mountaineering. He was the first person in history to ski down all 54 Colorado 14,000-foot peaks, has authored numerous books about about backcountry skiing, and has skied from the summit of Denali in Alaska, North America’s highest mountain.