My goal is to have to remember to bring as little as I possibly must. Loading my car at the beginning of the season with the gear that will live in my car is one way to accomplish this.
We always have folding chairs in the van. We have two adult sized and three child sized chairs which are removed only for use and then returned. My husband keeps another in his car. That way if he meets us at the fields or takes a child to a different park to a game he has a chair for himself, but if he’s with us we each have a chair.
Both of us always have a blanket in the car. The blanket is good for hot days when siblings prefer to sit on the ground instead of a chair. The blanket is good for cold days as a windblock or something to snuggle up under. The blanket is best kept there.
During soccer season, a soccer ball is generally kept in the car. Baseball season has the bag with all the bats and gloves and hats and helmets. The bag is easily moved from vehicle to vehicle if necessary. So far, we haven’t found it necessary for each child to have their own.
The final thing is a practice we follow, but I can’t recommend it because even the Red Cross tells you not to do it. We keep a flat of purchased water bottles in the van. Inevitably, no matter how hard I try, someone will need a water bottle for a game and has left theirs at home. Officially, the plastic can leach into the water making it not safe. Unofficially, having an emergency water bottle I can hand to a kid at the field can be a lifesaver.