I keep my eyes open for little bottles of water or fruit juice under the 100ml limit so that they don't get confiscated or in worse case scenarios I will buy a bottle of water once through security. The other alternative is to take an empty bottle with you and fill up once you get through security. In the States you find water fountains around to fill up your bottle however most places will give you tap-water for free. (I don't actually drink tap water anywhere leaving me the option to bring the small bottles or buy in the departure lounge!)
As your metabolism reacts differently to digesting food at altitude than on the ground I try to eat simple and easy to digest food for breakfast like fruit and yogurt or maybe an omelette for lunch or supper knowing that you will get fed about an hour and a half into your flight.
Meal tip: pre-ordering the vegetarian option means you will be guaranteed to get an easier to digest meal (kind of the lesser of the evils really).
So to keep hunger at bay when travelling I like to have a few snacks in my hand luggage (carry-on in the USA) like:
Small packs of Ritz crackers or Pringles crisps,
Dried fruit or fruit wraps along with a bar of your favourite bean to bar chocolate,
The list is really endless of what you could take. Another one I like is:
I also like to take my own green tea bags or red bush tea bags even though I am a devoted coffee drinker. Caffeine, red meat and alcohol are the things I try to avoid when long haul flying - over the years I found I felt better when I did that.
So happy and comfortable travels. Leave a comment below what snacks you like to pack.