Make sure you have enough fuel when driving in The Highlands, the average rule you can stick to is fill up when your tank is still half full.
Pit Stop for Fuel
Coming from the South you can stop in Ullapool at Lochbroom Filling Station and when coming from the North, you can fill up at Scourie Filling Station.
Also Lochinver has a fuel station and you pay for fuel using card payment (recently installed to the fuel pumps)