I would make the assumption that everything on your person and in the pack will get dunked. EVERYTHING. And if I'm wrong, that's great.

I also think that a pack (waterproof) tied in to the canoe is mostly O.K. , but having been separated from my secondary "kit" in one canoe capsize situation, I will ALWAYS have the basics on my person. I use one of these on a belt, and if necessary one UNDER my T-shirt (so it won't hang up - - had that happen too!)
http://usstore.aquapac.net/explore-by-activity/watersports/belt-case-uss828.html

In this regard, you stated you might carry insulin, needles, swabs IN THE PACK. I'd strongly suggest not. On your person would be more prudent.