This will be tough cause you won't be able to pack any snacks or juice cups prior to the gate due to security. Doesn't mean you can't bring an empty cup to fill behind security or hunt down snacks (probably unhealthy ones) as well. Also depending on the flight you will know the toddler's schedule best and if it is near the nap/bedtime I would recommend trying to keep them perpetually worn out so they are more restive in general in regards to travel. You'll probably have some lay overs in various locales so try to make any stop into a fun adventure and roll with the punches. Toddler balance is best achieved by focusing their attention, this is harder the more hungry, tired, or uncomfortable they are. So keep that in mind.