It really depends on you- for me- it did NOT work. I'd stick to 1500 calories a day during the week then not really count on the weekends (thinking I was doing well) and every Monday I'd be the SAME weight...
I don't know what you are doing but you can't pack say a health bar and water in your bag? Or bring a sandwich somewhere with you? You can't bring a small cooler?
If you eat out at a lot of restaurants you can ask for things like salad with dressing on the sides (dip the tip of your fork into the dressing and then get some salad), you can ask no oil be added to your food, no sauce/light sauce, stay away from the breads, drink water instead of soda, etc.
Say you make your three day break an eat anything deal (even if it's small portions) you could offset. If your goal is one pound a week, that's 500 calories a day you must have a deficit (3500 calories for one pound). And say in that time you get that deficit for 4 days and the other three you break even? Well at most you'll lose half a pound if you don't do any exercise- but if you aren't watching your sodium you'll retain water and might see that you aren't losing. And say you don't break even- say you actually eat 200 extra calories a day for three days, then you probably will see no movement on the scale.
I'm not trying to discourage you- but let you know how easy it is to see little/no progress if you diet 4 days on and 3 days off. A lot of times weight loss is about working harder than you normally would to lose weight- and if that includes preparing more food and taking it with you- then I'd do it. Even when I travel (I've got a business trip this week) I try to make the best choices I can and occassionally bring snacks/foods with me so I won't eat anything else. I've taken flights and brought food- nothing liquid- and haven't had issues.
I'm leaving Tuesday night to fly up North and I plan on eating dinner before I go the the airport (my flight's at 7:40) then whenever I get to my destination and get to my hotel I'm going straight to bed. My breakfast will be something low carb from the hotel (omelette most likely) and lunch I'll try to find a place that serves healthy food and stock up on veggies and protein, I'll get dressing on the side
. You CAN eat out and lose weight- but you have to really stick to it- specially with temptation in your face! Eating small portions won't work if you order burgers and fries and drink soda and so on