To open their first-ever show at Austin City Limits Music Festival, Dexter and the Moonrocks tossed a box of Cheez-Its into the crowd. “What’s up, f—ers?” yelled lead singer James Tuffs by way of introduction, before the band launched into a cover of “Song for the Dead” by Queens of the Stone Age. Against the heavy, high-energy electric-guitar riffs and thrashing of the drums, I spotted the bright red box of crackers bobbing up and down in front of the stage, where the band’s most enthusiastic fans, who’ve seen this long-standing bit before, were happy to participate. It’s impressive that four guys who got together in Abilene—26-year-old Tuffs, 34-year-old bassist Ty Anderson, 26-year-old lead guitarist Ryan Anderson, and 24-year-old drummer Ryan Fox (who goes by Fox)—have amassed…