Other than food, blankets, cookware, etc......
Some things have already been mentioned above, and there is certainly a lot more that can be added to this list..
Cribbage board, cards, a few simple games (Yahtzee, checkers, chess, backgammon, etc) water shoes, a few water related items (air matts, etc) Frisbee, ball and gloves, kids toys... I always have my fishing rods, tackle, fishing and boat licences. Basic hiking gear and maybe some kids plant and wildlife books. Our kids loved to identify things on the trails using their books. Paper and drawing related items for the kids. Outdoor carpet, chairs and an outdoor table. extra 5 gal water jug and siphon hose (if you boondock). Jack and tire wrench. Spare 12v fuses. Air compressors, one for the tires and one for the air matts. leveling blocks and wheel chocks.. Basic tool set, hammer and assorted screws and nails, tent pegs, nylon rope and a tarp. Hot dog/marshmallow sticks are a must... OHH and bug repellent, LOTS of bug repellent.... and anti allergy medication, just in case of reactions. First aid kit.
Bicycles, if you have a way to carry them. Portable fire pit and propane tank, for fire ban season. Aircraft cable and padlock, to lock items when you are away from your site.
We have solar on our trailer but also cary an inverter generator to charge up our batteries when solar or hookups are not available.
Also a fresh water hose and pressure reducer, and a sewer hose, water bucket and rubber gloves.
The list goes on and on, depending on your interests and or needs.