Never. I can't stand the crowds and the loud music. And I don't appreciate the crowds singing and screaming on top of the music either. I've been to concerts like two times in my life just because others insisted so much I joined them, and the experience was exactly what I thought it would be.
I'm just not cut for them.
I don't think I bought band related merch ever, but I've seen some really cool stuff so that is something I would consider if the opportunity presented itself.