Craft1948 can't have been to Kings Cross lately. The station is being redeveloped and there is currently no pub at the station. Further, while there are various take-away outlets (including Burger King) you have to cross the road to find McDonald's or any other 'eat in' place. (There's one branch of McDonald's almost opposite the station entrance, just off to your right as you leave, but I find it easier to turn left out of the station and cross the road to the McDonald's you'll see in front of you).
If you're looking for a pub, turn left out of the station, then left again alongside the station and first right. There are several bars along there.
Alternatively there's a really nice pub (the Betjeman Arms) within St Pancras International station, which is just across the road (to your right) as you leave Kings Cross station. There are also other eating facilities (including Carluccio's, which serves Italian food at reasonable prices) with St Pancras International.
Chris