I don't think I have seen such frighteningly bad advice in my life. OK, the author is young, but still ....
You will notice that up until this point, I have purposefully ignored the existence of cash. That is entirely because cash is the devil, the purveyor of wanton expenditures. Cash sitting in your wallet is begging to be spent, like an itch you can’t quite reach. It is easier to control your spending when it isn’t in cash form. Don’t believe me? Think about all the times you started your day with £50 in your wallet and ended it with zero, then can’t recall where it went. That’s pretty much all the time. Keep it to a bare minimum.
That is worrisome. You have cash in your wallet. You need to buy the days food and top up the gas tank. You know how much you need. Take that, plus an extra score for special offers.