Hi Jane, at a carvery, I tend not to have a starter and just load up on the stuff I can have for very little points.
Also, depending on where you go (I go to Toby), if you ask them for some veg with no butter, they will get them for you. You might have to wait a bit so I always ask when ordering the drinks as you sit down.
Meats are all ok - and the veggie gravy is not as fatty as the other stuff.
Other than that - enjoy yourself...xx