You've been going strong with your healthy eating plan, but then -- from reasons unbeknownst even to you -- you suddenly find yourself in line at a fast food restaurant. Don't panic. Everything is going to be just fine.
As you make your way up to the counter, look confident. Don't show any signs to other customers or staff that you don't belong there. Just breathe normally and smile. You may be tempted to protect your cover by keeping things simple; that is, ordering by number. Resist this temptation. Instead, look the person at the counter in the eye and tell them that you'd like a grilled chicken sandwich. Plain. Ooooh ... what temerity. How dare you walk into their joint and order something plain. Well, you just did, and judging by the stone cold look on your face, they'll know not to question you. But then, just when they think you can't possibly turn their world any more upside-down, you're going to ask for a side of mustard. Since mayo and ketchup have a fair amount of either fat or sugar, you're going with the yellow stuff. Again, don't flinch or show any signs of disquietude.
Next, they'll probably ask you if you want a meal or just the sandwich. This is probably a test to see if you're the real deal or just some health narc working the fast food circuit. Look them dead in the eye and say, "Yeah, make it a meal. Only, I don't want fries. Give me a side salad." Now, at this point, don't be surprised if people start dialing friends and family on their cell phones, telling them that they think something's going down and that this may be the last time they ever speak with them. Good, now you have them scared.