As pp have said rinse the sauce jar with a drop of water to make it go further.
Do the same with shampoo, conditioner and washing up liquid.
Only buy dilute juice for the kids rather than cartons/fruit shoot or fizzy pop. Lasts ages.
Go to bed earlier at night so the appliances downstairs are switched off earlier and there's no extra cuppas/snacks going on.
Reuse my teabag. Only I drink tea in our house and I like it weak so I'm happy to use a teabag twice.
Buy dried milk substitute and coffee mate to save on buying milk. Lasts ages.
Buy Kenco coffee refill packs from One Below. 23 cups of coffee for a quid - and I make myself one in a takeaway cup for when I go into town/out with the dogs. Saves on buying one for £££ while I'm out.
Only shop at Lidl and go either early in the morning or in the evening when things have been reduced. It's best when there's a ton of bread products reduced because it's all freezeable. I get everything for 20p each (bagels, scotch pancakes, crumpets, loaves etc) and end up with enough for 4-6 weeks or more and I've only spent a couple of quid. Bargain.
I never waste food. If there's bendy veg in the fridge I make soup. I turn any stale bread into breadcrumbs or croutons. And I only take notice of use by dates on packet and fresh meat. Cheese and eggs etc I use until they've gone.
Fix things rather than replace things.
Anything that looks like it could make a nice stock (peelings, chicken carcass etc) goes in a bag in the freezer. As do egg whites if I've only needed to use a yolk. And red wine. I don't get it often because it's a luxury so if there's a drop left I bag it and freeze it to go in a sauce or casserole at a later date.