I had 2 gym bags completely full of stuff.
Squat/dl bag - contained 2 sets of briefs and my squat suit, belt, knee sleeve, knee wraps, clamps to get into my suti and briefs, big bands towels, But then again, I bought my own monolift for the gym. When someone asked if I owned the rack, it was always funny to see their reaction when I told them I did.
Bench bag - bench shirt, small belt to keep the shirt down, small bands, wrist wraps, elbow wraps. Sling shot or bench daddy, towels, chalk.
And always a couple of extra shirts.
Luckily, for the most part, I had the opportunity to lift in a couple of great niche gym and build my own at the house. I think for the most part we were always pretty respectful.