Remember to use resources like ACCC graphs and Motormouth to find the best time to fill up in your area (only Perth has regular weekly cycles any more, every other major capital city has variable 1.5-2.5 week cycles). They say you've got 28 days to use these up (I find it's 29 days), so if you do a shop on Sun Oct 21 you'll have up until close of business Mon Nov 19 to use it.
Effectively you'll save $1.10 for every 10 litres you buy (seeing there's a minimum 4c available at any time).
Edit: credit to rekabkram, who says that you can buy 4 litres of milk for $5 when you pay for your fuel and get an extra 4c/L off. Therefore, if you usually pay $1/litre for milk, you make a 4c/L saving on every litre from the 25th onwards in one transaction.
Edit 2: Pdf not working for everyone, uploaded screencap
Note it does start on Monday despite the rest of the catalogue starting two days later.
To save 15c per litre on fuel at CALTEX WOOLWORTHS co-branded outlets, simply spend $100 or more in a single transaction (no transaction splitting is permitted at point of sale) at Woolworths Supermarkets from Monday 15th October 2012 until Sunday 21st October 2012 and surrender your fuel saving docket or present your Everyday Rewards card (not applicable in Tasmania) at any CALTEX WOOLWORTHS co-branded fuel outlet. Offer not available at Woolworths Liquor / BWS or CALTEX WOOLWORTHS outlets. Fuel discount valid for 28 days after purchase. Discounts not available on purchases of LPG at designated CALTEX WOOLWORTHS co-branded outlets or on any Caltex Starcard purchases. Woolworths Limited reserves the right to at any time suspend or terminate this offer. Regular fuel discount docket conditions apply. Purchases of Gift Cards (including iTunes cards) do not contribute to the qualifying amount. Smoking/Tobacco product purchases in New South Wales, Queensland, South Australia, Tasmania and Australian Capital Territory are excluded from qualifying amount by law.
I'm sure everyone knows by now but if you spend $5 you get an extra 4c off - Great for picking up 2x 2L of milk for $5 (you only need to buy atleast 25L to pay supermarket prices).
Also love 5% off thanks to the entertainment book gift cards.
I know for myself this between the 15c off, milk and gift cards I'll save over $10 off petrol this week.