For Bob's personal hygiene, I wanted to keep things simple, light, and inexpensive as the total price of the rest of his gear is starting to look scary.
My choice: Snowballs!
It's the perfect product for the ultralight winter backpacker. With a bit of ingenuity, Bob can use it to replace toilet paper as explained in vivid detail in Mike Clelland's Toilet Paper Free expeditions. He can also use it for refreshing "snowball baths" to avoid hiker's funk. It might even work as a hand sanitizer, though its anti-bacterial efficacy has yet to be approved by the EPA (or his hiking companions). Finally, Bob can build a windscreen out of them to protect his stove from wind while cooking and use one to scrub out his pot when he's done with his meals. Available for one billion years. Cost: zero. Pack weight: zero.