FULLY cooked food will be fine almost anywhere as long as it is served right after cooking. Beware of water that is not served in a sealed bottle (ships' water is perfectly safe). Beware of raw foods. Drink beverages prechilled, not in a glass with ice cubes (again not a problem on the ship).
Places where cruise go that would have safe water and food would include Bermuda, Aruba American and British Virgin Islands. Food and water will generally be safe at the MAJOR resorts almost anywhere .