Tax avoidance schemes, including the corporations (Starbucks, Amazon and the like) - I don't really care if they feck off elsewhere or stop trading in this country
I'd go through the local councils like a dose of salts - nobody would be getting £300k salaries there, and if they don't want to do the job for less I'd find someone who did. Nobody in local government agencies needs to be earning twice what the PM is.
I'd go through the NHS and look at middle management and admin, not frontline services like nurses and clinics. I'd make it so that if my elderly mother comes to visit me from another country and needs a doctor and a prescription and wants to pay for it, like she did, there was some means of her actually being able to pay. And once there was the means for someone like her to actually be able to pay, I'd make everyone else in the same situation pay. I understand about reciprocal healthcare, but when I went to Australia, I had to pay and was happy to do so when my son needed a doctor. Why can't we do the same?
Winter fuel allowances, free prescriptions, free bus passes for RICH pensioners, like they do in Australia (my parents have been stripped of their right to these things as they are too wealthy, and rightly so, and they agree that its rightly so).
That would be a start.