If you are looking to stay close to Fenway and not trek to the other side of Boston, Trattoria Toscana is very tasty and well-priced. They won the Best of Boston Affordable Italian in 2007 & 2008. Also, they do not take reservations, so you don't have to worry if the game goes over. It is a nice restaurant, the service is great, and food definitively superb!
I recommend this restaurant often and have never been disappointed.
If your friends are not as enviro-conscious, able to bring dinnerware, or you simply don't want to make them do so, consider buying a lot of cheap, machine-washable dishes, like these http://www.preserveproducts.com/produ... , which are themselves recycled and USA-made!
I'm going this route when my stockpile of plastic and paper finally runs out :)