Airport and on-route food is overpriced (3-5x normal) and poor quality. Snacks from home — nuts, fruit, sandwiches, energy bars — save £20-40 per traveller per long day and produce better travel mood.
What works
Hard items that survive luggage (nuts, dried fruit, jerky). Sandwiches eaten on first leg. Pre-packed fruit. Refillable water bottle through security.
What doesn't
Anything that needs refrigeration. Liquids over 100ml through security. Items prohibited by destination customs.
Five minutes of packing saves significant money and substantially improves long travel days.