Why not to create a competitive game mode where player can play as a team with his friends against another team . For example , who will be able to get maximum points by the end of the game for producing something from wood and all the vehicles which you can unlock on the map will be attached to the team which found them, but there will be a limited number of opening vehicles per team in one match ?
P.S. This is just an idea how to make the game more interesting and how to bring something new.