No Spend Days - not even milk (obv this needs a little planning, and transport to work doesnt count, buut leisure travel does). Staying out of shops, and off shopping sites - even browsing - stops you seeing something you didnt realise you needed til just then.
I keep a list of all the storecupboard things that I buy and then before shopping I check the prices online and through MSE forums for "price glitches". I buy in bulk when things are on a very good offer (less than half price)
Check for discount stores in your area - poundland etc, and independant ones - we have a charity one nearby, and while you need to watch the dates, Ive got stuff for 90% less than its selling in the Tesco 5 mins walk away. Its helpful to know the prices of stuff before going to poundland, as some things are actually slightly dearer there than in supermarkets.
Also, we switched to Quorn as part of my weight loss plan, and as well as liking it as much as some meats, its cheaper. (3 packs for £5 at tesco atm, and one does a meal for 4. since theres only two of us, its a bargain!)
Plan ahead and be aware of sales. I think that now is a good time to get oil, since demand, and therefore price, will rise from October. I bought mine this morning £510 for 900l, but hope to not turn on heating til end of october.
If you want your child to have a trampoline or particular outdoor toy, look now during the sales and put it away til next year.
In last week I signed up to MusicMagpie.co.uk and sold off a load of dvds and cds. While I didnt get much for each, when I factored in ebay costs and the fact they might not sell there, I went with the magpie site and got just under a tenner.
Also, signed up for shop and scan panel, but was on waiting list for 2 years or so. Only done first scan so not sure how itll all work out.
Valued Opinions is a good survey site, but many wont be bothered Id imagine.
TopCashback.co.uk for all online purchases (but also check nectar site)
Home based entertainment, or when meeting with friends, going for a walk or for coffee instead of dinner and a movie.