These are all great ideas, but even better still would be a kite boarder specific cart.
I ended up getting a dolly you can fold, but it’s pivot point makes it more work to push, and the smaller size wheels make it more challenging to push through soft sand. It also takes up a lot of room in my trunk.
Maybe most people don’t have to walk too far when kiting, not sure on the stats, but I sometimes have to walk 2.3 klm to get to where I need to go to kite. I sometimes just bring cold lunch and drinks, but that still means a small cooler, 2-3 kites, board and towels. I have also been known to bring a little BBQ that I can fit and tie onto the cart to cook something hot for my breaks.
I have also seen carts for kids and mountain bikes used, but I don`t see them working as good with all the stuff I bring.