Frank's advice is solid and conventional wisdom.
In whitewater one is usually with a group, and so your companions should almost always be able to get your boat unless they are all completely unprepared and unskilled in basic river rescue.
However, when paddling milder rivers alone with tripping gear, the risk of boat loss goes way up.
With a kayak I would do the same thing as a canoeist: attach painter lines of about 15'-20' long at each end of the boat. I use high strength 3/16" floating polypro rope, which you can get at NRS. This is not survival rescue rope, but will do the job of towing a canoe or kayak to shore in mild river currents.
With an open canoe you can just leave the lines loose so they spill out after a capsize. Alternatively, and especially with a decked hull, you can coil the lines under a bungee for quick deployment. The 3/16" rope coils and stows more easily and efficiently than 3/8".
If you capsize on a river, you will usually be right next to your boat, so you can grab it. Get to the end, pull the rope out from under the bungee, and try your best to swim-tow to the bank. If you can't do it, you can just let go and hope for the best. Having the rope attached to your body probably wouldn't help.
You may want to practice swim-towing, as there is an actual technique to holding the line. People do it different ways. Maybe there is preferred way now.
Classic Freestanding Rack
URCHIN Portable Anchor
Touring Kayak Paddles
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