Great subject! I typically paddle on lakes and bays since I am alone most of the time. I carry the same equipment every time; in the pockets:
Three SkyBlazer Flares, a quality (glass) signal mirror,a storm (loud )whistle, an LED (waterproof, luxeon=very bright) flashlight, a piezo lighter in small watertight cylinder, a small pack of energy gel,an icom VHF radio, small pocket knife.
Attached: top quality sheath knife (one hand release) strobe, towline(in pouch on small of back)
I also have a "safety sausage" which is a brightly colored orange tube designed to inflate and stick up about 4' from the surface of the water. It rolls up to a small size and has an opening to insert a lightstick which makes the whole thing glow at night.
I've been meaning to explore the laser signal described by Chris Cunningham. It sounds like a good investment.
I also am thinking about a quick release tether from paddler to the bow. Chris Duff has said he uses such an arrangement whenever the wind is great than 10 kts. Good enough for Duff=good enough for me!
The bottom line, especially for solo paddlers is survivability when the unexpected occurs. I've drawn bemused looks from folks on the water when they see what I carry. While I've not had to use any of this stuff, I've rescued many folks who have. I flew air-sea rescue for the NYPD out of Floyd Bennett Field in Brooklyn until I retired in 2001. The USCG had a base there until about 1997 (CGAS Brooklyn merged with CGAS Cape May to form CGAS Atlantic City). As a result, the NYPD was called to augment the USCG response to offshore incidents.
I can attest to the fact that finding a person bobbing about in the water is a very difficult task. A means of signaling potential rescuers greatly increases your chances of rescue.
If you beomce separated from your boat