Congrats!

You might check the contents of that Coast Guard Kit, and its price,
against building your own from scratch at Boater's World or West
Marine. Particularly as it isn't a "throw in" with this boat.

Upgrade the fire extinguisher.

Be sure to stow some sort of anchor with maybe 40- 60 feet of rode.
(your brakes in case of an engine malfunction). You can get a small
boat set-up that will sit under the bow in a carrying bag until the day
you (hopefully won't) need it.

Think about a first aid kit. Not as big a deal if you're never more
than a couple of minutes from the boat ramp and there's a kit in the
tow vehicle....but even so.....

If this is a first boat or you are going to be venturing into the sound
for the first time, pick up a copy of Chapman's at a marine supply
store and let that be your bedside reading for a while. Better yet,
sign up for a USCG Aux or Power Squadron course.

Above all, have fun. That's why you bought a boat. :-)