I actually have the same kind of feeling that longer you survive, less you need to eat and drink etc. Maybe distance you travel has something to do with that too. Worth staying alive then a bit longer. Last night I played for 5 hours and was gunned down eventually but while I run from NEAF to Devils Castle and then to NWAF I didn't need to drink nor eat as much as when I started my journey. Actually I drank and ate only once in that trip.