Drakes Fisheries in York does nice gf fish and chips to eat in or take away. They are right in the middle of town, so are convenient if you are visiting or shopping. I am a regular customer
They also have restaurants/takeaways in Knaresborough, Harrogate and Ripon and takeaway only in Leeds and Bradford but I don't know whether they do gf so you would need to check.
97 Low Petergate
York YO1 7HY