Sainsburys do a deal where you buy a drink, and chocolate bar for £1.
Oasis is 97p a bottle, and the chocolate bar goes through the system as 3p to make the £1 deal.
They also have a deal on with 2 bottles of coke,oasis etc for £1.60.
If you buy a mars bar for example with the 2 bottles of drink, it comes up as 3p extra. You can have one for every drink you buy, so 2 drinks and 2 mars bars would come up as £1.66
Its not advertised, the lad at the till told me the loop hole and mentioned it working with snickers and malteasers for example. I imagine any drinks, and any chocolate bars in these deals would work together.