Have you considered an ACR Firefly or the ACR Lifevest Signal Light ? They don't stand up on the deck of your kayak, but the reviews of the Seattle Sports Hydrostar don't seem to indicate a high build quality. Either of those lights with a good headlamp illuminating what you need to see would be both reliable and give a bit of redundancy. Both of the ACR strobes use 2xAA batteries, headlamps come in AAA or AA flavors.