I did the trip in July/Aug 91.
Most of the trout we caught were probably 14-18 inches. All were skinny suckers though. We really killed them while hanging out at Red Wall Cavern one lunch time. Eventually the fishing types got bored. It was not elegant dry fly type stuff.
I think the red ants are native fire ants (not the imported super-nasties). Which reminds me - bring your own stash (a few tubes/sticks) of sting-EZ. Trust me on this. You'll appreciate having it handy - and by the end of trip other people will offer you money, goods, "services", etc for some of it.
The water in elves chasm is warmer than the river. And besides, you don't really hit the water until after flying through the air where everyone can see you
You won't need huge headlamps. On the tiny side the BD ion and Princeton Tec Scout are in the 1 to 2 oz range. Slightly bigger - the Princeton Tec EOS and Aurora are in the +/- 3 oz range. You probably won't need anything bigger than these. Take a few headlamps, plus batteries. Between after-dinner stuff and reading you'll use them a few hours a night. And trust me on this too - if you have a spare to share, by late in the trip when people's flashlights are dying, someone will offer you even more money, goods, or "services" than they will for sting-EZ
That is unless the raft co brings extras for folks
The best place to save weight and space is to carry a super-lightweight synthetic sleeping bag and a lightweight thermarest.
Oh yeah - and banadanas - and tinactin type stuff - and for hikes a fanny pack that can hold at least a quart water bottle (inside or clipon).
One other thing worth noting - the big motor rigs really make many of the rapids seem pretty small. It'll probably be the big ones like Hance, Crystal, Lava, etc that get your attention. On the other hand, the scenery and the hikes will be more than worth your while.