Even if you've requested it, assume the vegetarian meal you ordered ahead of time won't be there. Most airlines do have juice available. Bring your own non-spill cup for them to fill. Hotels and Motels Ask for a small refrigerator when you make your reservations. Many motels and hotels have these, often for free or for a nominal charge.
Some places even have microwave ovens or stoves in a few rooms.
It doesn't hurt to ask. Even if you do minimal cooking, it's nice to be able to refrigerate snacks and beverages and heat up food for the child who is hungry before it's time to go to the restaurant. When traveling with children, room service can be worth the extra cost. If your children have been sitting all day in a plane or a car, they're not likely to want to sit calmly at a restaurant. Finding a restaurant with a take-out menu is another option.