Try to keep the hubs and BB out of the water as much as possible, even if they have cartridge bearings.

Do you have experience in fording deep rivers by judging their flow? It's not something to be toyed with, as a moderate to fast current will sweep you away, even if knee deep, and if you get trapped underwater on the upriver side of a snag, you won't survive. This happens a lot in Australia with fresh-water anglers.

I would suggest an inflatable mattress (of the old type that you blow up and are not self-inflating). You can then float your items across. Also, I would suggest taking with you a long piece of rope to tether you to at least one shore should you get into trouble. A ship's chandlery should be able to help with something that is lightweight, strong and of a thickness that will suit your needs.

It might seem being overprepared, but from what you are implying, I would prefer to be overprepared rather than underprepared.