Frozen food/fruit platters/sandwiches or other easy food.
Try and get someone to look after activities for you so you can do food, or the other way around.
Save present opening till everyone is sitting down - maybe at cake time.
If its at your place relax your rules a little about shoes on inside otherwise the kids will spend all day taking shoes on and off.
If you want the kids to wash hands before eating just use a bucket of water outside so they don't all have to crowd into the bathroom.