If you follow a more standard low-calorie diet and eat ~400-500 calories per meal, you can often make fast food work by ordering a kid's meal. Another idea would be to order a single small sandwich without fries and with diet soda or water.
This may not be a satiating meal since it doesn't have enough fiber, but something along the lines of a McDonald's hamburger plus a diet coke would be a "normal" thing you could order while on a diet and still stay within your calorie limits.
The key to it is distributing the food and eating certain type of foods that are very filling. If I'm hungry, I will eat, I can't think properly otherwise.
So I eat about 4 apples throughout the day (different fruit in summer), that's 200 calories. Fruit is probably the key since it stops hunger. For breakfast I have a cup of milk and 30g of carbs, which is either a slice of bread (no sugar) or some no sugar cereals. I'm looking for an alternative to the bread/cereals because it's not very filling or satisfying. That's roughly 200 calories.
Launch and dinner are 130g chicken breast, a lot of veggies. Chicken breast can be replaced with avocado or fish or beef, just keep it at 160 calories. I also put a drop of evoo (extra virgin olive oil) in the salad, half a teaspoon, otherwise it's really hard to eat (60 calories), so that puts the meal at roughly 250 calories if you account for some calories from the veggies.
Total of 900.
I also drink enormous amount of water while on this diet, it helps a lot.
Third day is the hardest, since the body asks for more calories, past the third something happens and body is fine. The major problem is at 4 weeks the body starts looking for alternative flavors, which is hard to do at low calories. Summer helps a lot because the fruit variety is incredible. Strawberries and nectarines are really good! If I save the evoo calories, I go for a bowl of ataulfo mango + nectarines + strawberries + raspberries, it's really sweet and filling.
I should also point out that I never eat at McDonald's either way, not sure what they put in the North American one, probably sugar, but after 1 big mac and 6 chicken nuggets, which puts me over 1000, I was starving. Did it once, would rather not eat than eat Mcdonald.