Not sure how much help this is...
But if you want an easy-to-reach place where you can see (usually) runway arrivals (but sometimes departures, depending on runway in use) with food and wifi, try the McDonalds car park near the South Terminal... I usually stop by while I'm navigating the M23
(Warning - 75min max stay, or a hefty fine!)
I also used to walk to one of the ring roads, right at the end of one of the runways... can't remember for the life of me how to get there though! - ???