I am studying at neither Surrey nor Southampton, but the course content across the board is fairly similar.
Regarding work... I honestly did not do much work during the midweek and very little at weekends. The only exceptions were for coursework and similar projects which were due on a near weekly basis for me (it was fine though, my university liked to give out a lot of small projects for certain modules instead of few massive ones). I only really started revising in the weeks leading up to the exams and I was able to get a 2:1 for my first year (A 2:1 is like a grade "B" and a First is like a grade "A". Typically a first is 70% and a 2:1 is 60% and so on). In the second year I will press on a bit more, but you just go at the pace which suits you. I don't see the point in finding work to do, I just make sure I'm on top of all my work and that keeps things relaxed. A benefit of university is that you'll typically get marks back every few weeks, so you know exactly where you're up to. That is my favourite bit about the assessments because I tell what my grade currently is and what I need to do on any given week.
Just remember that the first year is typically either not counted, or not worth masses towards your final degree. It might be worth 10% or so at some universities. For me, the first year is not worth anything towards the degree. Thus, you really shouldn't worry about it. The first year is usually to get everyone to the right standard. Some people say "the first year only exists to get you into the second year", and that's fairly accurate.
Not drinking is really not a benefit and not a negative thing either. The problem is not drinking, it's excessive drinking and the knock-on effects it has. For instance, being hungover during lectures or missing assessments because you're asleep. In moderation, it's absolutely fine. Even if you decide not to drink, it's important to try and remain social... There are times when you just cannot wait to get a piece of coursework or an essay over and done with and you need something to look forward to. Likewise, joining a society is a great idea... I go away on some weekends with my society, so it's a nice way to cap off a project. You need rewards, even if it's not alcohol related, find something to do with your time.
The labs are quite different to what you do in physics. You'll do thermofluid and solid mechanic labs in the first year. You'll investigate things such as the effect of a venturi or how a bridge operates. The labs are far larger (they're the entire room, usually a basement of a building) and you'll just go through the investigation as a group. We then made a presentation based on this and presented our findings to a lecturer and were then asked questions about the experiment and facts about the lab. Your mileage may vary on that one though.