For accesories, Id say a fishing rod, small tackle box, needle nose pliers and a buttpack to hold it in, a net that will slip under front bungees, a rope or bungees to attach to paddle, stringer, water bottle.
Make sure you sit in the yak in garage with gear and imagine you just hooked a fish, and go through what happens next, what you will need and when and make sure everything is easy to get to and tied down to the boat, yet out of the way in case you roll and have to do an exit without getting hung up on anythings ties.
Also ziplock baggies for cell phone {i double bag that}, and wallet.
Maybe legal stuff, here we dont have to register yaks, but they require a mussel sticker. Air horn for signalling boats that cant or dont see you. Lights if required for after dark fishing.
Congrats on new yak!