I have a big backyard as well. One occasion I brought out a laptop with a large screen and there's no interest in watching outside. So I have a fire pit, you can buy anywhere. That with some music and your all set. If people want to watch movies they can go in the house.
It's more like a mini party! Woo!! I have a really big backyard, so uh... I don't really know how to plan a party? It's for about 5 people, so um.... What about outdoor movies? How much would a home movie projector cost?