This is what I go by as far as lights are concerned. This is from the Coast Guard's Navigation Rules and Regulations Handbook...As far as I know, that's it for daytime use. Obviously, a safety flag for high-traffic areas is a good idea as is a whistle or horn and you're required to have a USCG approved 360 degree light at night.
The few times I'm able to get out these days are generally spent on rivers. That said, I carry a small ditch bag with the basics I'd need in case I unexpectedly had to spend the night and some first aid supplies, too. I have an 8 liter dry bag for all my overnight/first aid supplies.
My reasoning for the ditch bag is the same as my reasoning for a winch on my 4WD ATV -- as long as I have it, I will never, ever freakin' use it and it will be a complete waste of money. Let me go out without it and some kind of crap will happen.