Take care in the supermarket

I have been taking extra care when I've gone to the supermarket to buy a few things that those few things don't turn into a few more. Every time I've gone in the last 2 weeks I have had a list of stuff to buy and I've stuck to the list 100%. Every time I see extra things that I could buy but I ignore them and stick to the list. I want to learn to take the impulse out of shopping and I'm sure that it will just take a bit of self-discipline and prior planning. I just wish I had some proper historical data so I could compare my new grocery bills with my old ones.