Fuel up at either Donnybrook Shell or Wallan BP. Both are on the Hume, no need to go into towns. You will use a 1/4 tank getting to the track from there, ish. Winton have BP on track, though it's $2/litre. There is a BP and Shell in town if you do need a top up anyway.
Best to be at the track by 7:00-7:30, not need to be there earlier.