We were able to get "Shore Lunches" on Celebrity Mercury and Norwegian Sky. We just asked if they had any box lunches available to take off the ship.
On Mercury we received two nice box lunches with sandwich, chips, cookie and an apple. On Norwegian Sky we ordered from the room service menu and they wrapped the sandwiches in plastic wrap. Actually this was more convienient. The Mercury's box was a little hard to carry around, even though it looked nice. We ended up taking the contents out and put them in our backpack.
On Renaissance they did not have this option and they seemed taken back when we asked if they could wrap the sandwiches. One day we ordered room service and wrapped the sandwiches in baggies. The Renaissance room service sandwiches were not that good so the next few days my wife would go up to the Panorama buffet at breakfast and bring back sandwich fixings from their European style breakfast area. The hard rolls, meats and cheeses made a good sandwich and this is what we enjoyed most of all.
We always pack a few plastic "baggies" for sandwiches and other munchies on shore.
Sorry that I could not be specific in regards to the Zaandam.
Monday Chat Host (And husband to a frugal wife)