Three things worth 'investing' in: decent tupperware and plenty of it, a Thermos, proper waterproofs with hoods.
Then you are all set for storing leftovers, harvesting free stuff and eating outdoors at any time. Maybe you are not like us, but a huge proportion of our wasted money used to be in cafes and eating out.
The blackberry crop is incredible this year. Also damsons. Haven't worked out how to use hips and haws yet but will try to do so!
I really wouldn't internet shop - get out of the habit of supermarkets if you can, unless you are incredibly disciplined. Markets are cheaper IMO, even if individual things are more expensive IYSWIM. Buy one decent butcher's sausage per family member and make a big stew with them with plenty of veg, rather than buying 20 cheap sausages at the supermarket.
If you buy magazines, do stop. They are not only expensive in themselves, but they are specifically designed to make you spend more.I love them but TBH am happy to not have them any more.
The only reward card I would recommend is Boots. Great at Christmas.
Generic painkillers are only 37p a packet, but well tucked away at the bottom of the shelf.
Consider car-sharing or getting rid of it (if you have one), although other transport is also expensive. I haven't cracked this one yet at all.
Have a 'mum's night in' instead of a 'mum's night out' (if you have these with local friends) and get each person to bring a couple of no-longer-needed books or toys to swap between you.
Plan for Christmas (if you celebrate it). Tell all your family that you are buying presents only for under-25s (adjust for your family) and that they shouldn't give you any. I like Christmas but this reduces stress enormously. Use children's drawings as wrapping paper/basis for cards. Use last year's cards cut up for gift tags. Avoid urge to buy more than one present per person.