The distance limit of a person hiking in the woods carrying a six pack or case of beer. Can usually be described as a pile of broken glass bottles and crushed beer cans. Almost always the same distance from the trail head no matter where you are hiking in the world.
"Well, we've reached the six pack limit, look at all those beer cans!"
"We've gotta make the six pack limit by lunch or we won't make it to the nice campsites."