Well Rattletrap,
There are a lot of good ideas here..... Now I just hope after all this stuff is stored you can still fit the family on the boat
I fitted out a new Toon last year, most of these have been covered:
- Sturdy knife with lanyard for defense against mis- behaving lines
- Extra line for when you pull away from a dock and your brother in law says "that was their rope, right"

- Extra anchor for when the first one is thrown in and you watch the end of the line go with it.

( and sand bars)
- extra sun screen. No jokes about sunburns

- trash barrel, with extra liners.
- I have a back pack that goes into the boat every morning; this has all the extra things glasses and contacts, cheap sun glasses, towel, shirt, windbreaker, hat, cash ( if friend's wallet goes missing at gas dock

. ), sharpie, pen, paper.
I'm sure you will enjoy your new boat