When I recently attended my GP's surgery on a routine matter I asked him to examine a small patch of rough uneven skin which had developed on my forehead. He diagnosed a pre-cancerous condition, and prescribed some cream to eradicate it. I need to apply a very tiny dab, twice daily, for a month. My (free) prescription issued me with two large tubes of cream - enough to treat my whole face for several months. There is far too much waste in the NHS, and medications can't be returned even if the tube is sealed.
As for items that can be bought over the counter, it's a pity that our GPs can't just buy in a stock from the local supermarket, issue them directly to the patient and save a fortune on 'middleman' charges!
I agree that those who can afford it should buy their own. I'm not well-off, but wouldn't dream of asking my GP for cheap items that I could buy for myself.