If you capsize a kayak, a standard technique is to lift the bow of the still inverted boat to empty the cockpit, then spin the hull to be upright. That's not an easy thing to do, but doable. Climbing in is a trick. An empty kayak will spin faster than you can climb, especially with a PFD on.
If you have prepared for this moment, one way to stabilise the boat is with a paddle float. You can easily build one by laminating layers of closed cell foam into a flat oval of about 12" long X 8-10" wide X 4-6" thick. Drill a couple sets of holes not quite as far apart as the width of your paddle blade. Run a strong bungee through all four to make two loops on one side of the float. The bungee wants to be tight and snug. Slip it over one blade of a kayak paddle.
Now, the aft deck bungees also have to have been prepared for this operation. Place one paddle blade (without paddle float on) under the bungee with paddle out at a 90 degree angle, with paddle float way out there in the water. This stabilizes the boat. Now comes the part you need to practice ahead oftime.
Getting into the boat is essential. Cold water will sap your strength and ability to think. You cannot be upright in the water and climb up on a kayak. Swim along side the boat, flat on the water. right next to your cockpit, facing aft. Kick and swim up onto the aft deck on the side of the boat with the paddle float stabilizing it. You can lean on a paddle, but not your whole weight. Only fraction of your weight can go on the paddle. Put your weight on the boat. Swim/slither/climb your chest up onto the aft deck, hook a leg over into the cockpit, and finish getting your legs and butt into the cockpit.
Carefully turn around, leaning toward the stabilized side of the boat. Sit down, collect your wits, and bail or pump out the boat. Only after you are calmed and ready, do you recover the paddle and start out again.
If you are on a river, this is likely impossible as current will carry you into something. High, breaking waves on open water will make this self rescue technique difficult or impossible. Summary: Don't paddle into something from which you cannot self-rescue yourself. Paddle with a buddy with whom you can trust your life. Carry an EPIRB with GPS integral to the instrument.
Or, another technique is to have a large insurance policy with me as beneficiary.
