Popular songs to cover for a gig? Soft rock/pop rock songs for a highschool grad party?

Me and my buddies are playing a gig at a highschool grad party in a week and we're shot for ideas. We're into more folk/indie rock but we want to play songs people will actually recognize. We have two voices, drums, a guitar, and piano at our disposal, but what would be some good songs? So far we have Boston by Augustina, Little Lion Man by Mumford and Sons, Good Riddance (Time of Your Life) by Green Day. We also want to do a song or two by The Fray and Coldplay, as well as a couple originals.