Also get your son and his friend to check out apps like Too Good to Go, Olio, Karma and similar services that are a way to buy late date/ready to eat food from shops, restaurants and hotels cheaply. Think of it a bit like formalised/app-based yellow sticker shopping!
My ds is in his second year at uni and finds them useful - sometimes they have things he doesn't like but he can give it to flatmates or friends on his course, and sometimes trade it for things he does like from them if they like it. Some of them you can book ahead of time so you can plan a bit better (eg a local one here is a hotel that you can pick up hot breakfast items that have obviously been left on their breakfast buffet - means the hotel can put more things out so it looks good to the guests, they get a little money and don't have to throw as much away.
I also encourage him to go to the supermarket and markets to get food in person - going around with a basket in hand, knowing he has to carry it home, make sure that he has some stuff in for breakfast and packed lunches, and managing food around training and matches home and away - are all an important part of developing lifeskills. And I say that as someone who has trained her ds to be a great supermarket shopper already - but he is used to me doing the cooking more. I know I can give him a list to get things for me that I want to use - and he will be great at getting it and at spotting that xxx is on nectar prices and he knows we are getting low on it or he would like it for his packed lunch tomorrow and that his favourite pizzas are on offer in Sainsbury's this week but Morrisons next week, so he is already a good way there. He just needs to practice the planning and cooking side of things now, I help and support with ideas and recipes when I'm asked and pointing to things like the Batch Lady's cooking for student series, but at the same time, now is the time he will learn most from having to do as much as possible himself. He's not big on partying or clubbing - he doesn't drink (seems to be a lot more common than when I was at uni!) plus he's quite shy, so only tends to go out for occasional meals and socials with his teammates, often before or after a big match or tournament. And as I would love him to get more confident and sociable, I'm only too happy for him to spend some of his money on going out - as for him that's a really important skill he needs to learn too.
Talk to him, keep on top of him keeping records of what he's spending each week and month - and practising budgeting. Make sure he is keeping track of what he is spending on the friend - if he is genuinely going to pay your son back, it's much easier to have a list of it on the go and update after each purchase - and to make sure the friend knows what it is too - so that he can't turn around and say I can't afford to pay you back any of it or say that it's too much or he never agreed but thought your son was being friendly or generous... Might be difficult or awkward but again - another life lesson for both of them! And it will be good for them to compare what they are both spending - is he wanting the same to eat as your son or is he happily eating cheaper stuff, drinking water rather than coke or beer etc? Also worth getting them to look at the Batch Lady on instagram/facbook/etc and how she manages to meal prep - starting small but working it out and planning what they like, what they want will help them both, especially if they are able to freeze some stuff as they go, doubly so if they are able to pick up cheap grub that is close to its use by date but fine to be frozen to extend its life.