Go for something that you know will be low synned.
A Jacket & beans will be syn free, ask them not to use any butter.
Or go for a salad and ask for any dressings to come on the side. Then you can choose whether to use it or not.
Or go for a steak/piece of gammon and change the chips for a salad or jacket potato. The meat may have some oil used to cook it, but I would maybe count 6 syns to be on the safe side (1 tbsp of oil is 6 syns)
Don't stress about it too much, I've done that loads of times and then it's sent me off track completely and I've ended up with a big gain instead of a small loss or even a maintain.
There is always something that you can have when you go out, where ever you go.