I agree with most above. You could have cut 1-2L of water and packed much lighter food (chicken breasts??).

I'm 5'8 and about 150lbs. Please don't take this the wrong way, but I think you're *way* under weight. I've been your weight, and naturally could just motor thru most any cardio (running, soccer etc). But the strength isn't there, and hiking with weight is totally different than running. I started bulking protein (eggs and egg whites, chicken, whey etc) and lifting heavy, and am much stronger now.