It really does depend on the event, but for the most part it usually is including for raves, but it will be searched by security.
Yeah, if you're outside it should be fine. Security might check it though.
A blanket should be ok, just be prepared to possibly have it searched at security.
Depends on the event. I went for Self-Help concert and it was ok.
From what I've seen everytime I've gone, yes. I've seen people sitting on blankets.
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