As an aside, a few thoughts re "packs dragging you down:"

That's not necessarily the case. When canoeing, I have turned fairly heavy backpacks into buoyancy-positive flotation devices. For example, you pack extra canteens and only fill them half full. You double-heavy-bag every item to keep water out -- but also keep air in. As a result, many old-time canoes would float even when completely swamped -- as long as the packs were tied in.

Some hard-core backpackers have adopted this philosophy for crossing rivers. Air mattresses, Therm-a-Rests, and even the classic blue foamie mattress can provide a lot of positive flotation.

So a heavy pack can in fact be turned into an asset, flotation-wise.

My $0.02.