I found backpacks, even those purpose-designed for fishing from places like Cabela's, were too fiddily to work with in a boat.

My last evolution so far, is a large shoulder strap carry, top zip bag used to carry large Plano boxes with room for a few more plus a few outside zip pockets for stuff. The extra room inside can hold a micro-rainsuit and a thermos bottle. The outside pockets carry various fishing tools. The bag sits on the deck and everything is accessible from the top.

Good luck!