1. In general, any 12-bar blues song that follows the standard I-IV-V chord pattern is a good call. Everyone will know how to play this.
2. Any blues song that stays on the one is also a good choice.
3. Any of the standards are also good (Bright Lights-Big City, Stormy Monday, etc).
4. Play blues. This is a blues jam. They don't want to hear your rendition of Sweet Home Alabama or Metallica favorites.