If you are not going to have time to shoot some practice rolls before you go on your trip, i would suggest going with negative over transparency. Like Tom said, negative has a longer exposure range than transparency. Good black and white will have something like a 10 stop range from white to black. Color neg will be more in the 7 stop range. If you go to transparency then you are probably looking at 5-6 stops at best, and if you go with one of the highly saturated films like Fuji Velvia, then you are in the 3-4 stop range. That short range can make for some really vibrant images, but it can be unforgiving.