Sometimes the first day can be a bit daunting. Some people dont seem to want to interact. If you come across people who brush you off.. dont stress as there will be friendly people its just a matter of finding them. Some classes are great while other classes are less social. Tutorials in week 2 are a good chance to get to know people better. Just give it time
as far as extracurricular ... there is a huge choice of clubs and sports as other people have mentioned. There is also usually a band/person singing on wednesdays on the library lawn (its great if you can bum around on the lawn but very annoying if you are trying to study near the windows in the library). There are cake stalls, revues and movie nights and lots of different things going on. You can be as involved as as uninvolved as you wish.
If you enjoy acting/dancing/singing or doing stuff behind the scenes the revues are a good way to meet lots of people. Personally im too lazy to do it but alot of people who do get involved say its alot of fun.
Yeh there is a pub on campus as well as pubs withing walking distance. Pool tables and booze are easily accessable.