What is your most used piece of gear, and how do you use it? What are it's multi-uses, when do you use it, what has it made easier, how has it brought you happiness, how has it liberated you, how has it changed your experience…yet, what one way does it fall short of perfect?
My backpack. I use a Gossamer Gear Murmur for the majority of my trips.
I use it on my back, though I have heard stories of some that use it as a front pack. Never really believed them though.
Multi-Use? Well, I use it to carry the rest of my camp gear. I like to roll it up at the end of the day and use it as a pillow. Sometimes, I use it as a bear bag.
I use it whenever I go on trips of less than two weeks. A pack is requred for backpacking, I think. Carrying gear is MUCH easier with one. When I head out I know where all my stuff is. Backpacking makes me happy. Liberated? Well, I have several others I could use. It holds my pad next to my back, keeping me warmer in colder weather. But, the pack is just really light. It saves about a half pound over my closest next size pack. I cannot say it has changed my experience too much. It makes it a bit easier to carry, being small and light. The same things, small and light, make it a limitation on longer 3-4 week trips. I need to carry a slightly larger pack, the MiniPosa, to handle the larger food loads. Or the old Trek for anything over 30 pounds(>4 weeks.)
Yup, you have to have a pack for backpacking. Though, a vest with a multitude of pockets works OK, too.