Lookiing at Winnipesaukee's list above I can only make a couple of suggestions.
1. I'd carry 100' of anchor line at all times.
2. I'd invest in a sea anchor (kind of looks like a cone shaped parachute). This would be used if your anchor and line line doesn't reach bottom, the wind kicks up and you want to maintain control of your boat so you put it out and it slows the boat down.
It's also nice to have when you'rre trolling for salmon in the spring!
3. Orange flag should be under need to have, not might want. It's a daytime distress signal. Put mirror, strob and chemical lights in that category as well. The NH Marine Patrol is not really supportive of flares, I can understand why but I still have them on board!
I strongly urge you to contact the US Power Squadron or US Coast Guard Auxiliary and have a Vessel Safety Check. Free, no report to law enforcement, you learn a lot.
One trick I used to use when I did those safety checks for the Coast Guard Auxilary is I'd deal with the man when going through the mechanics of the boat, but when it came to the safety equipment I looked at Mom!
As I went through the safety equipment, the one thing I absolutely recommended to Mom, and dad because now he's looking at me like why am I talking to her, is to practice life jackets!
When you get to a sandbar, or back to the cottage at the beach, break out the life jackets and throw them in the water. Then make it a game, a contest with the kids....who can put them on...correctly...first? A race.
Make it fun for the kids so that if and when they ever had to try to do it on the water in an emergency, at least they'd have a clue, and so would Mom and Dad. Winner gets ice cream!
I don't know if anyone actually did it, but every Mom I pitched that to thought it was a great idea.