If the music is played for people other than invitees at a private gathering, permission is required. Most composers sign with ASCAP or BMI; the venues where music is played pay those entities, who in turn pay composers. Payment of the ASCAP or BMI fees entitles on to perform any and all music written by ASCAP or BMI composers with no further permission required.
If a composer is not signed with ASCAP or BMI, the composer would retain the right to decide if and when he wanted his music played. Enforcing his rights would generally be difficult, although he count prevent the DNC or RNC from including it in a broadcast.
Well, that depends on if the rally or the local beach has any firearms ordinances in effect. If you have a safe enough backstop, the albums could be stood up on a typical wooden frame. If you are facing out over open water, it might be reasonable to launch them with a clay launcher. I suspect CDs would fare better going through a clay launcher. Some nice #7 shot would do the trick.