Sounds like a ton of fun.
Topo maps of the entire route & a GOOD compass, not the 7$ Walmart/target/dicks compasses.
At least 100' mil5040c paracord
Pocket knife, ~3" one hand openable
Filet knife, if you intend to fish at all
Small hatchett or survival saw (two total for the group)
Ability to carry 2L purified water (one days worth)
Water filter (or tabs, filters are immediate though)
Cathole shovel (if you dont know, ask mr google - also, dont "make catholes" within 100' of water sources, and if you bury tp, animals are likely to dig it back up - it is generally not recommended to do so. Mix dirt around with the contents when done to aide decomposition - this is to prevent spread of desease, not to hug trees.)
GOOD rain gear, like toggs
Camping food, like mtn house, for the trip & 2 days extra
A multipurpose pot, where you get 1 pot and 1 lid/skillet. Bonus points for a pot with a spout. The stove should store inside it with fuel, assuming an iso pocket stove.
I prefer pocket iso-butane stoves. Just pick one you like and be familiar with its operation and cleaning procedures, there are so many options here it is rediculous. I can give specifics on my cook gear if ya like.
A fire starter (like magnesium rods or similar)
A cigarette lighter (Bic, not a cheapy one)
(May want to consider vasoline soaked cotton balls as fire starters, youtube how, I think that is silly though)
An LED headlamp <-very important
Another flashlight (or a compact battery lattern)
Extra batteries for everything
A first aid kit, and not the cheap preassembled jazz. Look at real ones (trauma kits or expedition kits), then go to a local pharmacy. 30$ later you are very well equiped. Don't take the heavy dumb stuff or all those ointment packs. Airway, breathing, circulation, deformaties, environment - prepare for those, not sunburn or ant bites. Don't carry gear beyond your abilities.
Something(s) to communicate with - PLB, amatuer radio, cellphones (not reliable at all, but better than nothing), etc.
Deck of cards, miniature ones are often at hiking stores
Small bottle hand sanitizer
Sleeping bag/fleece throw
Seems like a lot, but I hike with that on my back in an unframed pack - it should fit in a boat, provided you have any bulkhead capacity behind ya. If it is class I & less you can just tie off dry bags to your boat - learn knots!. I also probably forgot a couple things, but that is a pretty comprehensive list.
Know the river ahead of time, any real rapids, and what they do dry or wet season.
Know how to read a compass WELL. Rivers always flow out, but that may not be the fastest way in an emergency.
It is very helpful if someone is WFA or WFR certified, or has other medical training for similar scenarios.
And most of all, know how to paddle & know your boat.
I so wish I could go on a float - it will be a lifelong memory, I promise. Make sure it is a positive one. So cool. =)