Will all due respect to Bill Mason, standard practice for paddling white water is to make sure your gear is secured so well that it stays in place in a capsize. On some western rivers it's required by the agency in charge. Even ones without white water. They don't want gear floating down their river. On loaded trips, dry bags replace float bags. They displace water. That only works if the bags stay in place.
Obviously, on a canoe trip with frequent portages, spending a lot of time tying your gear in would be impractical, but I'd, at the very least, run one of the packs straps over a thwart or yoke and make sure there aren't loose items, like sponges and maps.
Around my neck of the woods, spraydecks are the standard practice nowadays for loaded whitewater.