Crosslands was a bar in Founders, it severed cocktail jugs, baked potatos, wedge, had a jukebox and a pool table, and it has now apparently been converted into a wine bar type thing. I will investigate when I'm back in the area!
No idea where you get RCS cards from, think I might have got mine from the picture gallery in Founders?
SU card is free, insurance (which you need) is £10 for one year or £25 for 3.
Very few places on campus accept debit cards, but there is a natwest right outside Founders with free-to-use cash machines (the union and medicine cash points will charge you), best just to get cash out from there!