Some good ideas already. Most of what you'll need is in your PSK. You'll have to tailor the provisions, food and water, to your expected trip, plus a reserve. I always like to ask the folks before we head out on a "day trip" if they are ready to spend the night if we need to. It makes you think.
Couple other random thoughts:
If you're on a tight budget, and don't want to buy a proper strobe, you can at least have a chem light stick attached to your PFD along with a whistle.
Be sure that you tie your dry bag to the boat... I have watched how quickly packs and dry bags can travel down a river. It's a depressing thing to watch as most of your kit rides down the river while you're tipped over on a rock... it's a mistake that you hopefully only make once, then get smart and have everything attached with a lanyard or straps <img src="/images/graemlins/grin.gif" alt="" /> That's also a reason to get a PFD with a couple pockets so you can have most of your gear on you.
You might want to have a spare paddle tied into the canoe, and some form of simple bailing device, even if it's just a cut off plastic Clorox bottle or something.
Also, have some line that you can throw, either to someone in the water, or to someone on shore if you're in trouble! They have weighted "throw bags" with line that pays out, but, you could at least have some lightweight floating line that has something that floats on the end of it, like a floating seat cushion, or ring.
Something that you don't take with you, but, is important... tell someone where you are going to be paddling in that canoe, and when to expect you back... when boating, we usually call that a float plan. It's always comforting to know that when/if you're overdue, someone knows that you're missing, and where to start looking.
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- Ron