Nike or Adidas crosstrainers, soccer/football-style shorts, and a t-shirt. And flip-flops and bare feet are stupid in a gym setting. If you drop a 45 on a shoe'd foot, at least the blood and bone fragments will stay in your shoe. But I don't want to be getting hepatitus from the idiot who shatters his foot under a dumbbell and then starts spurting blood around the gym like a damn fire hydrant.