How big a suitcase can u bring

You can bring back packs and small cases.

Backpack, a few on our boat were dropped off at a lodge up the river and they only had backpacks.

Its a day trip. I brought a backpack. With a jacket. They provided wool blankets for return trip. Can get cold.

Only a backpack or bag its a day trip so you won't need much

Yes

Whatever you can carry