I've been using this Pentel 8500 for a while now. I carry a pencil in my pocket at all times, and I'm impressed with its durability and ability to resist snapping under all the bending that a pocket pencil goes through. It fits the "thin pencil" requirement, but the plastic barrel is just a wee bit slippery, and I have a tendency to let it slide out of my hand when I'm not paying attention to it.
Time to fix that!
Step 1: Stuff
-Pencil. Surprise, surprise. Or a pen, I suppose, but I only use pens with caps, so this wouldn't really work.
-Sugru. A 5g sachet is more than enough. Pick whatever color works best, I used black on a dark green pencil.
-Alcohol and wipe of some sort. If you've used the pencil before, it has your finger oils on it.
-End effectors. Hands work well if you have them. If you're a robot, try a grapple or grasper.
-Work surface. The residue seems to wipe off my desk without a problem, but for rolling it out I put down a piece of glossy paper. Waxed paper, aluminum foil, plastic wrap would probably work equally well.
Step 2: Prepping
First, wipe down the pencil with the alcohol wipe. I don't know if this is really necessary for good adhesion, but it can't hurt.
Knead the Sugru to get it flexible, it doesn't take long. 30 seconds or so is plenty.
Prepped! Wow, that was easy.
Step 3: Apply
Very carefully stick one end of a snake to the end of your finger, and poke it onto the pencil. Then gently lay down the rest along the pencil. You can ease it out a bit to stretch it thinner at this point. Two layouts are shown here. The first is on my favorite pencil, it's hexagonal in cross-section, so I put a thin line down every other side. The second one is round, so I wrapped it around in a nice slow spiral. I found that it lays down flat if you lightly run a finger down it; on both sides first to get it to lie flush with the surface, then down the center to mush the peak that squishing the sides forms.
Tada! Beautifully grippy pencils that are still radially symmetric, and aren't the size of hot dogs!
Step 4: Leftovers
I used the leftovers to replace a missing foot on my tape dispenser and to rubberize my reading lamp so it won't slide around on my mini-fridge nightstand.