When I take the morning ORD to LHR flight, I'll often pack a lunch because I find two salty, carb-heavy coach meals on AA leave me feeling horrible by the end of the flight. Among some of my favorites, all of which can be packed the night before:

• Poached chicken with a side container of tomato chutney (presliced)
• Baby carrots and grape tomatoes
• Sliced apples
• Mini chocolates
• Unsalted almonds, cashews or pistachios
• Pre-packaged string cheese
• Energy bars (I prefer the Zone variety, because I find them more palatable and lower in calories than many of the protein bars on the market)
• Beef or turkey jerky (watch the sodium, but can be a good option if you're worried about being able to get enough protein while on the road, however, be careful if you're crossing international borders and there are meat restrictions)