This time of year most local rivers will be in the cold water immersion temperature range. If you fall in, getting out of the water is the first of your problems. Hypothermia is an immediate threat. It has happened to me & always surprises me how quickly the feeling of cold and shivering sets in. In the cool air of late fall drying even synthetic clothing outside takes hours.
I carry a few items with me; a knife, a flame red survival blanket, a candle style lighter and a whistle.The 3 weigh next to nothing and are not bulky. I have practiced whittling slivers of wood and lighting them with a sustained flame and it will work. You can't get a sustained flame from matches. The whistle can help alert S&R of your location. A flame red survival blanket will make you more visible.
Also many smart phone have some immersion rating. I always keep mine in a ziplock bag. You can also buy purpose made waterproof pouches or cases. You can't call 911 with a dead phone.