Supermarkets are best for fuel as they are several cents cheaper than normal petrol stations.
Was just about to add that myself, we used the Tom Tom to find the large Leclerc, Supermarche etc etc with Petrol stations (POI's as Fuel stations on Tom Tom), most were automated and round back of Supermarket car park.
Motorway Fuel prices for Diesel were 141.9 to 147.9 (Cheapest was 141.9, most were 144.9 last month when we went), if you come off the motorway and use the large stores the cheapest we got was 125.9 and most expensive was 129.9 (Average was 127.9) so saves you 12-19c per litre, we were driving from Calais to Mont Blanc (540 miles each way) and managed to save 30 Euros doing that, it does not sound much but at the local Aldi/Lidl about 20 minutes from our apartment (I forget which it was) you could get a box of 20 x 250cl beers for 6 Euros so we had 100 beers instead of paying motorway prices
As others have said, Hi Vis in the car (We had them on Parcel shelf and got 5 for £10 delivered) and 2 Breath Testers (about £4), Warning triangle and First Aid kit are part of most modern cars anyway but best to check yours!