I've always planned that Princeton Tec EOS headlamp I carry when out & about outdoors has a blinking mode that is rated for giving blinks of the highest brightness for 116 hours on a fresh pair of AA batteries, so I've always figured I could use that.

The only negative is that it is somewhat directional ... so it would be best pointed at a target. Something translucent and light colored (patch of white t-shirt/underwear?) could make it viewable 360 degrees, but would decrease the brightness.

I also have a red Rescue Laser, but I don't carry it with me on every trip.