Bench press and other weight machines mean nothing to me.  The best exercises you can possibly do are against your OWN body weight.
ie. push-ups, pull-ups, sit-ups, etc...
When I did...  It was for high school wrestling some time ago.  And I put put up about 125 lbs.  Didn't dare go any more...  I usually stayed around 95 lbs to get a decent workout.  I wasn't looking to max out...  If you get a decent daily workout your plenty strong, and you don't need to go tearing your muscles more with that added stress.
Backpacking...  I have no idea.  I've never felt the need to weigh my backpacks...