A few things I've learned whilst living on the cheap...
Check the ingredients when comparing products, even in the same range. For example, my supermarket's own brand handwash and own brand bodywash have exactly the same formula, but the handwash is cheaper when you check the price per 100ml.
There are false economies. Cheap washing up liquid is a waste of time and money. I've tried a few and the grease they dissolve starts to form a film on the top of the washing up water. Everything you wash ends up slightly sticky, even if it wasn't to begin with. Let's face it, you won't be washing up that often, so buy something bombproof like Fairy and be sure to get all of the mould and bacteria killed!
Beware of cheap stock cubes/granules/concentrates if you're making stew, chilli, soup etc. If you check the ingredients, most of them comprise mainly of salt. A more expensive version will be tastier and healthier.
Don't automatically think that "special offers" are good value. Last week my local supermarket had a deal on boxes of 100 tea bags. On the next shelf up was a box of 200 of the same brand, which would have been 20p cheaper than two "special offer" 100s.
If you're cold, put more clothes on. Sounds basic, but I don't consider putting the heating on unless I'm wearing tights and two pairs of socks under my jeans, plus two shirts a fleece and a hoodie, and I still can't get warm.