Take snacks on the plane, whilst you cannot take food off the plane with you once you reach your destination (if its international) you can take food on to the plane. Sometimes it can take a while for the flight attendants to reach you with food, so this way you can feed the kids whenever they are hungry.
This also prevents meltdowns when the kids do not like what they are served by air staff. I also take an empty drink bottle onto the plane with us. Whilst you cannot take water onto most planes, ask the flight attendants to fill up the kids drink bottles once you board.
One of the first things we do when we reach our destination is to do stock up on snacks and bottled water at a local supermarket.
We keep our stash in our hotel room and back our day bag full of goodies before we head out each day. Kids are always hungry at the most inconvenient time, like when there isn’t a shop in sight or you have just commenced a 5-hour bus trip or something! And don’t forget to fill up those drink bottles each day too so you are not forever purchasing bottled water.