Bring some insect repellant and sun tan location.. Bring all your drinking water and cooking water. It can get very windy even in the canyons. Carefully plot where and when Lewis & Clark camped going up and down river and bring their logbook writings for those days for fun. There are plenty of small hikes that we did. Open canoes - fine, whole trip was just fast water, cold, we never even thought about swimming. The weather can be hot or cold, and you can be wind bound. Bast part was down river of Coal Banks Landing, look it up, there is a small settlement with a very nice general store/outfitter - we rented our canoe there.
Within the first hour a deer jumped in the river and swam accross right in front of us. We visited Indian teepee rock rings and many homestead sites along the river. The people at C B L loaned us a 3 ring binder detailing all the natural and man made things and sites along the river. We went just a bit later than your trip, to camp at the same locations that L & C camped at on the same calendar dates. The river was deserted, we saw, maybe three small groups the whole trip.
After the trip We $ had the people at C B L shuttle us back to C B L, stayed in their VERY interesting collection of original homestead cabins and celebrated with them the 200 year anivarsay of L & C expedition camping at C B L.
Whole trip esp. when viewed from the historical nature of the L & C expedition was great fun.
We also visited some L & C sites on our way to the river, Fort Mandan, Knife River Indian villiage etc.
We brough water because one easy, 2. Cheap and 3. We wanted to eat fresh as possible on this no portage trip so we started out with frozen jugs of water in an oversized cooler. That's what the people at C B L suggested would be fun. The trip is far more of a "float" than an rigorous paddle trip.
We had lots of time on the shore to hike because the current makes it easy to put miles over land quickly.
Might be a fun place to try sailing up river of the wind is right.
We took turns reading out loud about the sites we were passing while drifting down river. Fort Benton is not much of a picture postcard type of place that's why we started at C B L. Fort Benton is a nice, a easily to be proud of place, if you live there.
With your number of days on the river you will have plenty of time to realy enjoy the hiking and solitude.
I suggest you put in late in the afternoon and camp the 1st night after just getting out of cell phone, road noise, and street light range. That's took us maybe 3 minutes but then we kept going to where we could hunt down some teepee rings on the bluffs (North side) above our campsite for sunset.
I am not used to canoeing with a cooler ever. That's why my dehydrator is a buzz 24 hours a day a couple of days ago. But we will be bringing a cooler for the long drive for lunches with 2 liter bottles of ice ( it makes things ever so less messy in the cooler) so if it fits.. and we can refill/refreeze our bottles , it's an idea.
The river certainly allows the paddler to leave Current civilization behind, but there are plenty of reminders - barbed wire, homestead shacks, buffalow jumps (if you know where to look) etc, of the past foot print of man. That's also why we did not pack like a northern Canada barrens trip. You can have the time to have fun with a Dutch Oven, we brought an Al version, for elaborate meal times for example.
Tie your boats down at all times, the wind can gust to 40 MPH from almost nothing in a mater of seconds. This happened once on our trip at night, we followed the instructions the canoe outfitter and did not have a problem.
I've only had a cooler on two trips, this one and a one week Maine trip down the St. John River.
Best advice I ever received "St John River, 2nd week of May, River will be high enough, well after ice-out, and most important BEFORE the black flies." Took a friend brand new to canoeing, camping, white-water and I decided to give him the professional guide treatment, lots of meat, steaks, chicken, fish caught by me out of the side streams, etc.
Update. We contacted the Bureau of Land Management who advised to carry water due to nitrate and phosphorous runoff. The outfitter also advised the same. I hate travelling with jerry cans of water. Just hate hate hate it. I think we may try the First Need XLE Elite water filter which filters smaller particles than our MSR filters ( which are fine for northern travel).. But I am wavering. I love buffalo jumps for tradition.. I have only seen those to which I have been guided to like Head Smashed In Buffalo Jump in Alberta.
But we may need those jerry cans of water for deadmen. I hear you on the winds. The winds on the Green wiped a tent( not ours) off our campsite. Yes we do have a guidebook featured on the history that has a map of all the Lewis and Clark campsites... Its time to go back in time...far back..
This year on the St John the advice is wait.. the ice out is going to be later in May. Another very very good trip.
The buffalo jump was the one mentioned by L & C, lots of bones, wolves, bad bad smell. It was a large cliff on the right/South side of the river. And of course we realized that all actual campsites they used have been obliterated by the natural meanderings of the river over the last 200 years, but the views from the river are relatively unchanged.
Have fun and we only experienced shoreline mud only a couple of times.
I paddled that stretch back in 1999. Filter the side creeks for water supply. May or the fall are good times to go. It gets really hot in summer, as in well over 100 degrees. Back then there were some commercial trips for the first three days and no one for the rest of the trip. The bighorn sheep didn't even left their heads if we just floated past. Bring the L&C Journal. After a couple of days we referred to each other as Charbonneau, Clark, and Patrick Gass. I named my mule Judith. It was a fine trip that made a powerful impression. I would do it again but not in July.
Livestock in the water crapping ( in herds of hundreds!) make side streams and the main stream unappealing. Mining runoff has left heavy metal pollution in the river and its not filterable. May was hot. Probably the better time to go but it was darn hot. 2014 floods cut the banks 10 feet high.. and muddy as all heck. Kipp Rec area and some of the campgrounds badly damaged, which led us to make the trip of 108 miles in 4 days.
Would do the trip again but not drive out of the way for it.