Like everyone said...hit the SF of the Payette. Both runs are great. I've done them at 3500 and 1200 cfs. Canyon run was a little grippy for a class IV boater at 3500 (and includes an easy must make portage...thats always in the back of your head). Both runs were still awesome and very manageable at 1200 cfs (late july). Think "Numbers" at the same level. There are mellower runs upstream of Canyon (class II+- III-). The Main Payette thru Boise can be class III or mellower.
There is camping all over the place on the SF of the Payette or near Salmon.
Biking!! I know Boise has some good stuff. But what you really want is Ketchum. This whole valley has probably the best riding anywhere in the US. Smooth, fast, flowing singletrack. Get the guide book for the area "Good Dirt: Sun valley mtn bike guide"...awesome guidebook. Ketchum is a gorgeous 1.5 hour drive southeast of Payette put-ins. There is also riding in the Sawtooths (in the guidebook) that is right near the town of Salmon (30 minutes from SF Payette put-in)