Hi, your kit looks good to me.
Since itīs for whitewater kayaking I would keep the kit light. But it depends on your boat and your style.

My suggestions so far:

- a small candle
- a magnesium firestarter
- Tinder-Quik tinder
- several small fatwood sticks
^^(I wouldnīt count on the Wetfire only. It can fail.)
- a map
- small backup knife

As for the shelter, you could improvise something using survival foil blanket, paracord and branches.