Re: Important stuff!
I don't know what kind of water you're fishing, or how angry a river it is, how remote you will be from help, or what the temperature is going to be like there, but if I were going to be fishing on a hairy river, way far out in the boondocks, here's how I would do it:
I would tie myself off with paracord and a carabiner to a floating dry bag. Tied off to it so that if the boat goes over, it's going to be with me, but use the carabiner and light paracord so that if you go in the drink and the bag becomes waterlogged or gets caught, you will be able to get shed of it to prevent drowning. A floating bag so that you can use it as additional floatation if you go in for an unplanned swim.
In that bag, I would have an extra set of warm wool clothing, a quality knife, 50' of paracord, a shelter half of some sort (this can be as simple as a plastic painter's drop cloth, an 8X12 sheet of the stuff rolls up as small as a woman's wallet. Shower curtains also work well), dry tinder and fire starting materials, perhaps one of those GPS distress signals, signal mirror, whistle, one of those emergency mylar blankets, first aid kit, any prescription medications you cannot go long without (insulin for a diabetic, heart medicine, etc.) some method for making water potable, some high calorie food such as protein bars.... that's all I can really think of for the moment. That very kit, sans waterproof drybag, resides in my vehicle, it's about the size of a carry-on bag for an airplane.