Here is my list of must haves. You will find most of it overlaps with the above mentions. I assume from your previous posts, you are planning a single day float of the canyon. This list only addresses day trip concerns.
R2 Safety Gear:
- PFD, helmet, and drysuit (or other splash gear) - all worn of course.
- Patch kit + top off pump
- Spare paddle x 2
- Dry bag: contains extra fleece, First Aid kit, headlamp, lighter, water-purifier, and extra food.
- Water bottle (attached via carabiner to a strap)
- Flip strap: I attach a 15' cam strap around the girth of the boat, allowing a quick re-flip if necessary. Very handy on big water R2'ing.
- Throw bag clicked to thwart x 2 (one front and one back)
- Pin Kit: (worn under dry suit or in PFD) 3 biners, 2 pulleys, 20' tubular webbing, 12' prussik cord.
For your trip, I would also include a full days worth (or two) of dehydrated food in a dry bag with my backpacking stove. Just in case
The only real difference I think in my list (aside from placement of items) is that I would always have a flip strap on the boat in case you get tossed in one of the bigger rapids and need a quick re-flip.
I've also worn a throw bag's worth of rope, but it's not comfy and given the volume of the Snake I don't think that will help you much if you truly wrap your boat. In that situation you are likely to need additional boats and assistance to retrieve mid-stream equipment.