What do Willie Nelson, Foreigner and Huey Lewis & The News have in common? They’ve all shared the stage with San Antonio art-pop band Buttercup. Vocalist Erik Sanden, guitarist Joe Reyes and bassist Odie are capable musicians and songwriters who also have a knack for onstage surprises. For instance, they might even make a sandwich on stage. Seriously. Former Spurs player Brent Barry is opener Panic! at the Costco’s frontman.