The first thing I would always budget for is rent because there is (unfortunately) no saving on that. Most people’s rent is between £6000-£8500 over the year, and therefore it makes up the most of their expenses. This is unavoidable, and so I always make sure to budget for it using my student loan, as I know for sure how much is coming in from that. However, the loan may not cover some students' rent, and so you need to make sure you have extra, reliable income, such as a part time job, in order to pay this.
The next major item to budget for is food shopping. I tend to budget £60 for a 2 week shop. I don’t often max this out, but it allows me to replenish staples in my cupboard (such as spices) as and when they run out without panicking about overspending. It also depends on where you shop, as places like Aldi and Lidl are obviously much cheaper, but as we live in the city, getting there can be more of a hassle than getting a food delivery from a more expensive store.
Once these have been budgeted for, I like to plan for fun activities such as meals out, pub trips, and nights out. These are things which are more flexible, because you can always buy more or less depending on your budget. Personally, I like to plan for £40 a month for pub trips (as I don't spend lots on alcohol). I then budget around £30 for takeout or meals out, as this doesn’t happen too often but I like to be able to do it when the opportunity arises. Something I find really helpful is to budget for Uber (or taxis) so that I know I can always afford a safe way to get home after a night out – it takes the stress of the money away.
Of course this strict budget can be quite difficult to stick to throughout the year, but I find that having separate bank accounts can really help. I have a Monzo account which I deposit a bit of money into before a night out and only take that card with me so I’m not tempted to spend more than I budgeted. This also means that I don’t take large amounts of money out with me.
Of course a budget will look different for everyone depending if you decide to get a job throughout uni, rely on loans, are supported by your parents, or work over the summer and save up for the year. It is equally important for everyone to budget, and try not to compare yours to anyone else’s, as you can always participate in the same activities just by adjusting how much you’re spending.