Chaz et al, thanks for discussing this topic, which is supremely important for anyone who actually goes somewhere with their kayak. Without the ability to reboard in a reasonable amount of time under difficult circumstances, you could be dead in short order if the water is cold or the waves are sending you onto the rocks.
If you read "Sea Kayaking Deep Trouble" (as I would recommend you all do), you will learn that a high percentage of deaths are caused by boaters' inability to reenter in difficult conditions. Of course, those boats were all sit-inside kayaks, which theoretically are harder to reenter, but the urgency of attaining skill at reentry is the same with a SINK or a SOT, so make sure you can do it—and practice safely in the most difficult conditions you expect to encounter. This is a central principle in all sea kayaking training.
Stobbo, I'm sorry I must take issue with your somewhat simplistic and exclusivist statements about how anyone should be able to reenter just by jumping back aboard or they shouldn't be on the water. Lithe or muscular or athletic people seem to not understand that reentry can be very difficult for more average people, or older people, or people a few pounds overweight, or relatively lacking in upper body strength--so would you really have all of us stay off the water? Roadrunner's excellent video of how to enter his Oasis shows how easy it is for him, but I'm going to hazard a guess that something approaching the majority of people reading these posts would not be able to do that even after practicing. I know I certainly can't because I have tried. I'm 58, of average size and build, 5-10 pounds over my ideal weight, not very strong in the upper body. It's a long way up and over the gunwale of an unloaded Oasis (especially with a good PFD) and it's very easy to pull the boat back over on top of yourself, especially if your legs sink like stone like mine do. My Adventure is a lot lower, but also a lot narrower. In any case, boaters should see for themselves in a safe setting and not assume it will be easy.
Although I haven't tried them yet, I'm betting swim fins would be one of the best things to have to help you reboard, although that's one more thing to carry and possibly lose in a capsize.
On both of my boats I have installed a kind of strap eye about 2 inches long just to the outside of the mesh gear pocket. To this I attach a 9' x 1" NRS cam strap, and I roll it up with a rubber band and store it in the mesh pocket. I won't go anywhere without it. You can use this strap as an already-rigged stirrup so you can use your leg strength to board. As cryder mentioned, arm strength will leave you first in cold water, so it's good to have a way to use your leg (one leg).
You can't simply stand up on the strap like using a ladder; the boat will tip over again. You still have to kick to get your legs roughly parallel to the water, reach across to grab the opposite side of the boat, and KICK HARD with the leg not in the stirrup to propel yourself onto the boat while you simultaneously shove yourself forward with the stirrup, i.e., more horizontal movement than vertical. It is best to keep the strap loop adjusted such that you have to tuck your knee right up tight under the hull (with your instep in the stirrup); this gives you the most horizontal movement, and you can sort of snap yourself back into the boat with practice. (I tie a loose knot in the end of the strap to keep me from accidentally pulling the end out of the buckle.)
The strap can also be used to help right the boat if necessary (righting is not so easy with an Oasis; those of us who can't just pull ourselves back into the boat will have an equal or greater difficulty climbing over the top of a capsized hull to grab the opposite gunwale or handle): throw the weight of the buckle over the overturned hull, move to the other side, and pull on the loop with your feet on the side of the boat. This is the same technique river rafters use with their preinstalled "flip lines."
Even with fins or a stirrup, anything that will help stabilize the kayak will be a welcome, and perhaps essential, thing. The Sidekick Ama will surely work well in this regard IF it is easy to quickly deploy. Paddle float systems, like most SINK users carry, can also work, though they do have their disadvantages. I use Harmony (Voyageur) sea sponsons. These are inflatable tubes (about 6" dia) that I keep clipped to the sides of my boats with two small strap eyelets above the water line. They are light, small when deflated, and inconspicuous when properly stowed, and pretty quick to deploy, but give a lot of peace of mind for reboarding (especially if exhausted), for really bad sea conditions, for stabilizing the boat for an ill or injured person, for relieving yourself at sea, or sleeping in your boat while tied to kelp or mangroves etc. The sponsons don't stabilize as much as the amas will, but on the other hand they are quicker to deploy and not as much to carry around.