Katie, that is an interesting question.
The thing with kayaks - being "self-propelled" type of a vessel, they generally do not require registration. That may vary from state to state, but in general - unless they have a motor mounted, you do not have to register it... And you would not have any of those formal requirements to carry VHF radio, GPS, etc... While it's a great idea for safety - it is not a requirement.
But I'm really not sure.
I would suggest that you put your question up on some of the more active kayak fishing forums, and I'm sure you'll get some valuable input.
www.bigwatersedge.com
www.jaxkayakfishing.com
Hope this helps, good luck!