We often do. The food is already paid for and in many cases I prefer the 'safety' of the ship food over island food but I'll admit to being very cautious when it comes to eating in countries I'm not familiar with.
We're going on a southern in January too. My preference is not to eat on the boat. I'd rather eat while we're out doing stuff and not worry about coming back to the boat. With that said, in Aruba we're going to Eagle beach and if we can't find a lunch place we will come back and have something on the ship.
So I see that some of you just stay on the ship after you come back for lunch, but do some of you leave again? We’ll definitely be looking to maximize our time in port so we won’t want to stay on the ship after lunch.
If we went in for lunch, our kids wouldn’t want to get off the ship again (ages 7,10,12,15).
We’ll eat a big breakfast before we leave but don’t always eat lunch in port. We’ll usually come back to the ship early (3ish) and they will have snacks poolside and swim before we have to get ready for dinner
Another reason I will eat on the ship (except at Castaway) is because I am gluten-free due to a wheat allergy, and that is not always easily accommodated off the ship in ports. (Obviously depends on where you are - Italy is amazingly easy. Greece was not so easy, even with an allergy card written in Greek by my Greek-American friend so I know it was correct.)
Any food allergies I would 100% eat on the ship (as I said, other than Castaway since that is Disney operated) to prevent any issues.