So...in the chippy.
- You can order fish and chips without worrying. Oh, but in and eat-in situation you may need to specify that you don't want lemon on/with it. Salt and vinegar are both safe (vinegar has...ascorbic acid? Mallic? Either way it isn't citric, and that makes all the difference here)
- Beef burgers are ok, (including the battered ones) as long as you don't get salad on it (yes, lettuce contains citric acid!). I am not sure about gherkins, so I'd play it safe. No ketchup (tomatoes!), so I'm afraid if you are getting this option you'll probably be eating it plain.
- Beware the sausages!! They might be ok, they might not. Best to steer clear.
- Pies and puddings: There are so, so many different issues factors here, What butter was used in the pastry? Are the pies fresh? If not, did they have citric acid added to make them keep? What kind of gravy was used inside them? To me it isn't worth the hassle.
- Sides.... well, curry sauce is almost certain to contain citric acid. Mushy peas are probably ok. Gravy is a chance; which brand do they use? If you ask they might have a package with an ingredients list you can study.