The welcome bag included a big calendar poster that you can put on your wall in your flat, freshers event booklet, a pen, sourz, and just other little leaflets I think....I really can't remember well as I picked up so much that day and was just shoving it in the bag as I went along lol.
Ermmm I think you receive like an accommodation book and stuff, with little guides about starting your first year.
I also got a 'starter' box when I picked up my keys for the flat, which included discounts off places.
But be aware, this probably changes every year so it may not be the same when you start.