Hi! I'm going to Mary's but I was actually at Van Mildert last year for a summer school! I found that it was actually a really nice college despite being less well known, the facilities are up to date and clean and the bedrooms were relatively modern and well designed with sinks, wardrobes, desks, big windows, beds and plenty of storage. The dining hall is gorgeous with lovely views over the college's lake (your room might too!) The ducks are adorable and there is a green perfect for picnics etc in the summer. The JCR and bar are both pretty big and each corridor had a fairly large kitchenette as well. Admittedly the bathrooms and showers were standard uni quality but I had such a lovely time there and I think it's a really lovely college!
In terms of what to bring it's up the individual. Bring bedding, clothes etc, things to decorate your room, fancy dress. I'm sure your college will advise you! Don't pack too much but think of it as moving into a new flat rather than going on holiday. If you have any other questions I'll try help but I hope that makes sense for now!