We supplied a little food (veggie platter, fruit bowl, cheese), a little beverage (beer, seltzer water), but primarily, we supplied a venue. The only entertainment supplied was a sea of plastic toys upstairs, downstairs and in the garage/driveway (well, some metal, also, especially the bicycles). And one antique wooden glider rocking horse. Guests brought substantially more food and beverage (you can tell, because we had more after everyone left than before they showed up), including some wonders like homemade strudel with vanilla sauce, and homemade guacamole.
My sister did a ton of the cleanup, including sweeping the kitchen floor. Extended family and friends helped a ton with watching the kids. All in all, a ton of fun and NOT too much work. We were thinking we'd do this twice a year. I'm going to try to do the next one in the fall and see if we can make this happen seasonally on or around the solstices/equinoxes.
Keep it in mind, should you find yourself within party-commuting distance of our place.