OK, I've just re-read the thread so now have a little bit more background info. Whilst I can still empathise very much with having out-of-touch baby-boomer parents, I don't think it's the issue here. Did it ever occur to you that your Dad is actually very much in touch, and trying to tread a fine line between:
a) making sure your food doesn't spoil or denying you the chance to bulk shop to save (by buying the fridge/freezer) and
b) enabling your financially destructive behaviour (£20 for petrol)?
If he had seen anything worth £20 in your recent purchases which were not absolutely essential then to be honest he's doing you a favour if he turns you down.
I see a lot of similarities with my one time best friend forever. He grew up in a wealthy household, had boomer parents who never had to worry about money, and did all the things he was supposed to do (uni, etc.). He really struggled when he set out on his own, dismal luck with jobs in particular. But he was also hopelessly disorganised, liked to stick his head in the sand about things, and retained this unshakeable belief that he had the right to nice things like clothes, gadgets, household goods.
I always thought that he was doing OK, up until the point he asked to borrow a couple of thousand quid (which, in all honesty, was small change to his parents) from me for an unexpected bill. It turned out that he and his housemate (joint owners, bought together to get on the ladder) had bought a DFS suite on credit, the interest free period was coming to an end and while the housemate had stumped up, my friend didn't have his half. This was not an 'unexpected' bill in any sense of the word - he'd signed up knowingly 18 months previously.
I knew what he earned and what his bills were, and that it would have taken three or four months to pay me back. Stupidly, I lent the money.
Three years later, when I had seen not a penny of it back, I visited him in his new rental home. He had abandoned the house he part-owned along with my the furniture to move in with his then new girlfriend several hundred miles away. This two-bed flat was kitted out entirely with new stuff, all on credit. Off the top of my head, there was a dining table/chairs, two sofas, two TVs, double bed, sofa bed, desk, microwave, pots, pans, plates etc. I'd say close to ten grand of brand new stuff. And please, could I lend him a few hundred to get his car back on the road?
We had strong words that weekend. He had asked me for the money three years previously because his parents had, in fact, refused to give him any more. He had maxed out his overdraft, and taken out a personal loan to pay off his credit cards, and would have defaulted on the DFS loan without my help. He had now taken on even more debt with his GF's support. He had actually invited me to stay because he thought he had bought some time by switching all his credit cards to a 0% deal on balance transfers, without realising that there would monthly minimum payments which were now running into four figures.
Long story short, the relationship was unhealthy - for me, and I am not at all 'out of touch'. I was enabling him. He wasn't bipolar, and not even unable to exercise any self-control, just unwilling to.
Like his parents had found, the only thing that worked was to tell him that there would be no more cash.
We no longer speak to each other.