I'm currently in the Peruvian Jungle trying to get to the village after the plan crashed. My play style involves trying to get everything done and then moving to the next area so I try and collect and do everything possible. Of course with games like this you can't always do everything, for example, I couldn't do the first tomb where the first base camp is because I didn't have the climbing axes.
I'm not sure if you can run back, I haven't tried and it's so far away I don't really want to but because of the jaguar encounter I doubt you can go back on foot anyway. So that leaves travelling between the base camps as the only option.
At what point in the game is travelling between base camps unlocked?