I have an icom floating handheld, thing is awesome, but there are others out there. Just make sure its' completely waterproof and will float. See JackK's story from last year and you will know why!
I always have a compass with me, not smart to rely on electronics to get you around. I also carry a strobe beacon and a whistle.
A signal mirror, air horn, and flares are not a bad idea either.
As for re-entering if it flips, the best thing to do like TDF said is to practice.
However, I recently come across this idea:
TopKayaker.Net - Paddle Float and Rescue-Stirrup Re-Entry for Sit-on-top Kayaks
which is a stirrup that could help in reentering a higher-sided kayak
the other really important thing to keep in mind is dressing for the water temps, make sure you have proper dry gear. Many of us wear the kokatat tempest dry pants with a splash top or dry top.
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