For 4 adults you should be looking at least for 6-persons worth of tent (2x3-man tents or 1x6-man tent). Inflatable mattresses (with built-in battery operated pump) are really nice. If its gonna be hot and humid then ditch the sleeping bags and bring cotton sheets and blankets (and pillows). Folding camp chairs are important (1/person). The full size, double burner camping stoves are nice. A good sized wash basin if your going to create dirty dishes and a some cheap big water blatters if water is available on site. They probably won't provide a picnic table so you might want to bring a folding card table (if you have room).