I usually just choose the healthiest option depening on the day I'm on. For example tonight I ate out with a friend and because I was on a red day I suggested we go to a steak house so I had a lean fillet steak with a large salad (no dressing) and half of the jacket potato that came with it as an HEB (with no butter or any other filling) I ate only half because it was quite big and even though half would have been less than an HEB I figured I'd be better of if I erred on the side of caution.
If I was on a green day I would have suggested chinese or wagamama and had lots of plain rice or noodles with some stir fried veggies in black bean sauce or oyster sauce. Or maybe an Italian restaurant for some pasta and tomato sauce and a large salad to fill up on.
Also whever I'm going out to eat I try to save an HEB to cover the oil in the food.
I always check the menu online if I can. Next week I'm going to Pizza Express, the week after Indian and the week after that is a Christmas Take That night with 3 course meal.
At Pizza Express I've found really the only thing I can have is baked aubergine, which I love. It would use 3 healthy extras in olive oil, parmesan and mozzarella. I'm guessing anyway. I dont use all my HE's every day so should be ok.
If you dont go too over the top with one meal you should be ok but you need to make the healthiest choice you can. Bloody difficult if you dont go out much like me, so I will struggle to pick the healthy option when I really want pizza!
The salads at Pizza Express are gorgeous, I'd choose those over the pizza anyway it is hard to request no doughsticks though lol.
I think the easiest way of sticking to the plan when you eat out is not to be afraid to ask for something to be served how you want it. Most restaurants are used to people with food allergies etc. so are quite happy to serve "off-menu". For example at Frankie & Benny's recently I had the bbq smothered chicken but requested it without the cheese, and extra vegetables (broccoli and carrot) instead of a potato side. At a couple of syns for the bbq sauce (served on the side) it worked out to be a very SW friendly meal. It does help to nudge whoever you're out with in the direction of somewhere that suits (McDonalds tends to leave you with nowhere to turn) but feel reassured that you can make most places fit in with the plan.