Two thoughts come to mind:

1. Personal Locator Beacon: If you are traveling alone during a trip that could indeed put you in harms way (running even moderate rapids would fall into that category), then I am starting this think that the purchase of a good personal locator beacon, though relatively expensive, should be seriously considered. My thinking is something along the line of -- picture yourself injured and hoping that someone will come along to help or that a friend or relative would finally notice that they haven't heard from you - what would you be willing to pay to get your situation resolved almost immediately? I think $600 or $700 isn't far off that mark, considering a nice mapping GPS can run $300-$400.

2. A few months back I had the good fortune of chating on the phone with Malcom Murray, the gentleman who makes the Rescue Reflector mirrors. He gave some great advice. First he recommended a mirror than can easily be held by one hand - specifically a 3x5 mirror, as opposed to a 4x5 mirror. We also talked about the quality of CD-ROMs as signalling devices since I was thinking of using them to teach signaling to a cub scout den. Based upon his measurement he found that they were good at all. He also recommended to avoid glass mirrors since they are so heavy and breakable.

Do signal mirrors need to have holes? It is very nice. While I don't think you necessarily need the higher tech sighting grids, the ability to sight from the center of the mirror can greatly increase your aim while using the two-handed sighting method. The sighting grid gives you the ability to aim one-handed, which is nice. On the other hand, the usual practice is to sweep back and forth across the target, so if you are peeking from one side of the mirror it seems the result is likely about the same. I'd rather have a high quality mirror with no hole than a CD-ROM with a hole.