I did this the first time this weekend and it was awesome! Many other have given pointers, so I'll just add on some things I didn't read about before going, or didn't take seriously.
- The river is not dirty, if you're used to swimming in lakes and rivers. This is much cleaner than most rivers I've been to!
- Don't bring anything valuable. Anything! We were even talking about bringing a cheaper cooler next time because we almost lost it.
- I agree that tying the tubes together is best, but there were a few times we got stuck on trees or rocks and being able to untie would have been helpful. I saw one group with carabiners that they could hook up to each other's tubes. Great idea!
- It is possible to not get burnt, just make sure to put sunblock on ALL your exposed parts throughout the day and don't forget your ankles, hairline, or swimsuit margins (oops!)
Have fun!