Great question! I have to say that for me personally, it's yoga all the way. I know there are probably hundreds of great answers to this question but for me, the stretch and range of motion involved in yoga really helps prepare my body for the inevitable stiffness I feel when waking up on backpacking trips. Depending on what type you practice, yoga can be pretty weigh-bearing too (side plank with one leg in the air, i feel that burn!).
I tend to favor more intense flow practices when I am gearing up for a trip, and stick with a floor based session like yin for a few days after any major endurance activity. I'll have to look up pistol squats and see about adding those to my pre-trip routine too. Thanks for the idea!