Before you start spending $ on lenses, I'd work on getting very familiar with the camera. i know the trip is coming up soon but try to shoot alot between now and then and carefully critique your own work. Even after years of shooting, I still learn and modify my techniques as I use my camera.
As far as lenses are concerned, decide what is your "must have" range. Again, if yo find yourself always wishing you could be closer, you need something longer than the 18-55. Or, if you wish you could step back farther a lot, you need something wider (although a panoramic technique can make do).
While certainly things like optical quality and faster apertures are considerations, I'd consider adding the EF-S 10-22 for wide and any of the 70-200's for longer. Tripods are nice if you use them and are willing to carry one, but given the size of your setup, something like a small Gorillapod or a bean bag might make as much sense. Then, get an extra battery, some extra memory cards, and finally figure out how you'd like to carry all this and you are good to go for a long time.