This planning usually pays off as I always have something healthy to snack on but I still find it frustrating that I can't just travel light and grab food as and when I feel like it. So in the spirit of taking a true holiday, including from my usual fastidious food planning, I took off to the states with absolutely no supplies with me at all ... And survived!
Ok so there were a couple of instances where I had to resort to unhealthy ready salted crisps as a snack (usually just potato, oil and salt so pretty allergy friendly). But generally I found it fairly easy to stick to my usual healthy diet without having to go out my way.
One place I usually never go without some snacks is the airport because plane food is both unappetising and rarely healthy, so that was probably the area I was most worried about. But I was positively surprised by my vegan meals - yes you can now pre-order a vegan or gluten-free meal on your flight but sadly not in combination so I had to eat some wheat, but I'd rather that than the usual cheese/cream laden gluten-free vegetarian food.
On the flight out dinner was rice with cannelini beans and veggies with some grapes for dessert, which hot doc stole as it was nicer than his nasty plane dessert, and the pre-landing snack was a filling and tasty roasted Mediterranean vegetable ciabatta. On the flight home dinner was pasta with ratatouille, again with fruit and breakfast was a granola bar with a banana. I did supplement all this with a packet of kettle chips and a bottle of water I picked up in the airport as you don't always get fed when you're hungry and I usually need more water than I get given.
Even if you're allergy/intolerance free ordering vegan meal is a great idea if you're flying long haul - you'll sleep much better after a lighter meal and feel a whole lot better when you wake up than if you'd had some rich meat or cheese dish. You also get more fruit and veggies that way, so more vitamin C to fight off your neighbours germs, and less calories than the standard meal so it's better for you all round.