Portland, Maine daytrip with kids

My wife and I are taking our family to Portland for a Saturday. We have baby twins (and gigantic double stroller) and a 3 year old.

We are meeting up with a group of friends to visit the farmers market, have lunch in Deering Oaks Park and go on a mailboat cruise. After that, the friends are going to have dinner at a grownup restaurant and we're on our own.

I'm looking for a good and relatively quick but not fancy dinner option (ideally takeout for a picnic, but eat in may work if there's room for the stroller) that would be easy to get to after the boat ride.

Also, if there are any places we should consider picking up food near the farmers market or park (or any farmers market stands that do great prepared foods for lunch), I'd appreciate recommendations. Wandering around with the little ones can be iffy, so I like to be armed with ideas when we go somewhere new.