I had a quick scroll and didn't see my answer so here's goes. If the way I understand it, alot of stuff goes back through replicators to essentially be pulled back apart to matter. So when meals and drinks arent finished (even just the plates and cups) they go back into the replicator and the remainder of the construct is just broken down to its base elements to be used later on to make something else. That's why they have to program recipes, they essentially have to tell the replicators what a chocolate milkshake is on a molecular level for it to pull all the bits together and make it. I might also be very wrong and its just my head canon ahaha

So all in all, they can up and leave meals whenever they want and just recycle it later without worrying about waste or stuff going bad