Boats, transmitter, lifting straps, tools, chairs, sunscreen. We have a collapsible wagon to carry it all from car to pond.
No spare batteries as my SLA's last longer than my endurance sitting by the pond. I leave the pond toolbox in the car, but take it in case of failed fuses, loose set screws, etc. Murphy's law corollary: If you don't have a tool you will surely need it.