From WordNet (r) 3.0 (2006) [wn]:
backpacker
n 1: a hiker who wears a backpack [syn: backpacker, packer]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
backpacker \back"pack*er\ n.
one who backpacks; as, two backpackers were mauled by bears
in Yellowstone this week.
[PJC]