In UK English I would say 2. The first sentence looks like it's missing an article to me ('a'), and the third looks like it's missing an object ('You want to order what for delivery?').
When at the restaurant, I'd say 3 or possibly 1. Or most likely a mix of the two: 'I'm here to pick up a take-out'.
Except in the all of the above, in UK English we'd say 'take away', not