You could use one or more coolers with ice. If you don't have any, you can get styrofoam ones very cheap.

I would also consider tweaking the menu to include fewer things that must be kept really cold.

We get those blow up baby pools, set them on the tables, fill with ice and just set the platters right on top of the ice.

Baby pools or any type of big coolers work.

If you had an ice sculpture person they can cut slabs of ice and set on a tray where the water can collect and then you just place your glass plates on top.

I've used kiddie pools, also. I specifically bought one of those cheap round plastic patio tables because it fit the pool perfectly. The pool/table combo holds about 5 large salad bowls with no worry of them getting warm.