As stated, there are lots of factors to consider. Hiking by myself, without as strict deadlines and turn-around times, I'll often carry a Kiev-88 body, 2-3 lenses, 2-3 backs, Technika 4x5 with 10-15 film holders, water and other essentials. In a group, maybe the body and one lens and 2 backs, OR my Moscow 6x9 folder (Zeiss clone). Protracted travel en famille, without our own vehicle, the 6x9 folder wins. Light, fits in a pocket or bag, quiet, almost large format. And the "finickiness" lets me still feel like I'm working a camera, not taking snapshots. I have some excellent shots of the moon over Paris, just with it sitting on the parapet of Pont Neuf. I also carry a little rangefinder (Kiev 4) pretty often for casual shooting.
To go in a different direction, I have also hiked, kayaked, dived with a Nikonos--depends on the activity. What I want: folding, lightweight, rangefinder 6x9 with coupled meter that is waterproof to 100m.