You can order anything off the room service menu at any time!
However, as Kuki said, be sure
that you're able to take food off the ship. Many ports forbid this. There will be a notice in the Caper's if you are not allowed to take food off the ship.
BTW, I'd be leery of taking a sandwich off the ship early in the morning for lunch! It's very
hot in the ports and you could get food poisoning. You should be able to find good, safe food in the port area if you're not adventurous