If a student needs to gain maturity I suggest this can be done through taking a gap year. DD worked a bit in London, then became a chalet host and then did Camp America and some travelling around the US. (The latter two seem to be recruiting UK nationals again for the upcoming seasons.) Really hard work, low paid, and lots of fun. She certainly came back with confidence and an understanding of how money has to be earned. Three years on and I think she still has some reserve savings from that year.
She is lucky as she does not need to work at University. Medical students who work, mainly as HCAs, are stretched. You are at University to get a degree and certainly in later years it is better to do that well, have time to expand horizons and start job search which can be enormously time consuming).
In terms of money we give DD about £75 per week. She can live on £30pw when funds are running low, but if you add in fares and extras £50 is probably the minimum. One thing to watch out for is the unevenness of spend. Freshers and the first term is expensive, especially sport which can involve subs, kit, match fees, gym fees. Exam terms a lot less so. Watch out for the universities whose term patterns are 2x12 weeks and one of six.
In terms of drugs, observation is that many students have spare money for either drugs or a lot of alcohol/taxis/takeaways, and it does not seem to correlate that well with parental income. Country lines mean that Class A drugs are easily available in every small town across the UK, so some kids, posh or otherwise, will turn up at University thinking ket or coke are normal on a big night out. Equally it means that others will have already decided that drugs are not for them. Parents will know their DC. Some are frugal, others like to party. Some are confident cooks, others will rely on takeaways. I would base decisions on what to give a DC based on what they might do with the extra money.
(DS was always likely to underspend and to save money, and worked in summer vacations. We got any extra money back effectively as he did not need a subsidy when, post graduation, he needed to pay a deposit for a flat and buy furniture.)
Again the first term is expensive. In her last week, DD was reduced to the chilli con carne that she had batch cooked at the start of term. It was easy for me to organise a food delivery to give her a bit of variety over the last few days. The next couple of terms on the same money were much easier.