To answer the OP question, smaller bags from multipacks NOT single bags are lower in carbs and fat Seabrooks are about 12g carb - sorry don't know the fats, also multipack bags of things like quavers, French fries, teddies, are lower in both too. Although they have other ingredients .
I used to have the occasional bag of multipack ready salted walkers as a treat but not every day and not with a sandwich etc as well.
I don't have a remotely sweet tooth and crisps are/were my Achilles heel - haven't had a crisp since beginning of January and haven't missed them at all