I think that depends on your definition of "willingly". I can think of a few examples, but you could argue the willingly part. For example:

1. You are some Special Forces/Recon guy on a mission. There are many stories of these guys carrying well over 100 lbs, and non of it includes tent, extra clothes, sleeping bag, cooking gear. The food is usually 1 meal a day. Ammo gets heavy fast, so does body armor, weapons, and communication gear. No room for personal comfort.

2. Hunters who kill something big and have to carry it out. Ask phat about this one, I only hunt rabbits right now.

3. A dad at the zoo who stays too long and ends up with TWO kids on his back (each over 20 lbs), plus the kid carrier, and whatever hubby put in it. I know this one from experience. <img src="/forums/images/graemlins/wink.gif" alt="" />

4. Someone living in a foreign (to them) country and who doesn't have a car, but needs to ride a bus to the store to buy food. A backpack is a good option, but man, all those grapefruit juice containers sure add weight. <img src="/forums/images/graemlins/laugh.gif" alt="" />

Like I said, "willingly" is used loosely. <img src="/forums/images/graemlins/wink.gif" alt="" /> <img src="/forums/images/graemlins/wink.gif" alt="" /> <img src="/forums/images/graemlins/confused.gif" alt="" /> <img src="/forums/images/graemlins/grin.gif" alt="" /> <img src="/forums/images/graemlins/grin.gif" alt="" />