I was going to bank the difference from grocery shopping but am finding that because we are already saving the 52 week challenge from our spending money, it is hard to save much more from there. If we have money left over from there it goes towards maintaining things which is another form of saving anyway.
However I compared what we paid in bills exactly 1 year ago to now (January 2014 compared to January 2015) and thought that banking the difference from there might be a good idea.
I had to pay our phone bills and gas bill and found that the savings there were $30.00.
I also noted that last year we were paying $90 per month for my car insurance. In April it fell due and because it dropped so much we could afford to pay for it outright (saving us from having to pay the $80.00 direct debit charge). I thought as it is due again in April it would be a good idea to save that money aside too.

So my first banking the difference deposit is $120.00.

To add that to the 52 week challenge would be $5,632.00 we would save by the middle of January next year.