Find out the cheapest day for petrol and fill up on that day eg. here it is Tuesday. Never fill up on a weekend or public holiday. I also plan my errands so that I get everything done in the one car trip with the least amount of kilometres.

Supermarkets also discount items at certain times during the day. You may find that towards the weekend or end of day butchers and grocers do the same. If you have a market near you try buying fresh food from there as they will also discount massively at the end of the day.