For some reason, when cruising, I ALWAYS start the day with a good breakfast and then plan excursions after that. By the time you return, unless it is some all day thing, you can go to the buffet for lunch or if a bit later, the afternoon snack. You should be able to get a sandwich after the main lunch time.
I don't think I would chance taking food off the ship, if you get so hungry, there is always local food in most ports...