off topic!
The reason that JK didn't want Coca-Cola in the shops is that those brands don't exist in the Wizarding World.
I've never heard THAT as being the issue. I have only heard that the issue is health.
And the issue with soda is the sugar, and in America (and almost nowhere else in the world) that sugar is HFCS, which is a horrid form of sugar. But then they use corn syrup in almost every candy they have. Sugar isn't awesome, but corn syrup and HFCS are worse to many people (I say "all" but many people don't realize they are having negative reactions to it).
And then the "potions" are just artificial colors and flavors put into water.

I asked a family if they were good; they said "well, they are sweet, that's for sure".
I've only ever heard of health as being the issue.
...but the types of dishes available at Leaky Cauldron impact me because I don't eat meat besides chicken and turkey. I at least have the option of a chicken sandwich there (after I remove the bacon); it must be frustrating for vegetarians/vegans.
It is, absolutely. I asked for their vegetarian not-on-the-menu option (as a TM told me to do) and she said "we have a salad and some vegetables". WOW. Awesome. That'll fuel me for a day in the parks. I asked about the ploughman without the scotch eggs and she said "oh yes". If I felt like asking specific questions about the cheeses I might have been disappointed, but when out and about I don't ask about cheese. At the store, yes. But at a restaurant, no. I don't eat parmesan when in Europe (by definition it has rennet there) and leave it at that.
Anyway, it was decent but not awesome. She did add in a bit more bread and a bit more cheese for the scotch eggs, so it was a meal for the 3 of us, but it did leave room for snacks later.
What's SO frustrating is that England and Ireland are *so easy* to be vegetarian in! I mean it's not even an issue. EVERY place has veggie options. England is practically covered in "suitable for vegetarian" signs and labels. Even in the timeframe she was setting the books in, at least in Ireland it was super-easy to be vegetarian (and therefore I must assume England as well).