Ah, the avoiding-excruciating-gallbladder-pain diet, I remember it well. My sympathies.
Avoid, or suffer the consequences: cheese, butter, oil, cream, chocolate, pastry, fatty meat like some sausages or pork. Usually safe: pasta, rice, potato (jacket, boiled, or mash without butter), white fish, turkey, lean ham, chicken, pretty much all fruit and veg. What passed for a treat as dessert was a meringue nest, fat free fromage frais, and raspberries. Or jelly. But that got old quite quickly!
Meals I recall eating a lot: jacket potato, veg, fish; pasta with veg/tomato sauce or lean mince bolognese; pasta salad or rice salad home-made for lunches (lots of veg chopped in, bit of very low fat mayo, tuna)... To be honest you can do very low fat versions of most meals if you're prepared to cook. I'm not a desperately keen cook but I managed it
In winter home made veg soups are good.
When desperate, marshmallows are very low fat (but obvs v high sugar so you know, moderation and all that...depending on the kind of day you've had). Hope you soon feel much better.