First of all I am sooo envious... how lucky to be going on two such wonderful trips...
I hope someone with more experience will chime in and answer your questions... I will be watching this thread with interest, I have the exact same set up you have.... I did however, just buy a used canon 28-135mm.. I am still getting acquainted with it... but so far I really like it, it is a pretty heavy lens though.
Next If I were going on these trips I think I would be looking at some far reaching lenses:> I would not want to get to up close and personal with many of the critters that live in either of these places...but would definitely want to capture some pictures of them... and a good tripod to boot.
Good luck and have a great time on your two trips
Rebel T1i, Lens EF-S 55-250mm, EF-S 18-55mm, 50mm, Canon 28-135 mm, PSE9 and 10, CS4