Assuming you have all of the normal safety equipment staring with a PFD, first aid kit, anchor, safety flag, hand bilge pump, etc, etc.
Then for my first accessory, it would be a fish finder/GPS combo and good 12 volt battery, for fishing in the ocean a portable marine radio, flare gun, landing net.
Since I live in the PNW, I also have a good "dry suit" for the cold water, rain, snow and decent undergarments that wick moisture.
I too have a PA-14, so my Hobie Trailex trailer makes storage and transport a snap.
Good luck with your new PA