I use a headlamp that I make sure is on when there are boats around. That, and I always have my whistle. It never gets taken off so that in an emergency I can reach for it w/out looking. One of the guys I fished w/ last night uses a glow stick on a piece on string. If a boat starts pointing towards him he spins the stick in a circle. It makes a big halo that's easy to spot.

Can't wait to go again,
Amish Ed