re: Big Bend Camping Info

camp up in the mountains, it's much cooler at night and there is a chance you'll find water up there. The hike to the south rim is fantastic, as is the hike up to the top of Emory Peak.
As for the flat land part of the park, go to the hot springs, and drive down to Santa Elena and Boquillas canyons.
I can't help you with the kayaking, except to say don't be surprised if there is very little water flowing when you go.

While there, go over to Terlingua, it's a cool little town.

Also, wake late one night or early in the morning and sit outside and check out the stars.