Both booker and Costco put things on offer ever month - these are the best times to stock up. Costco typically have the best deals, but Booker sometimes do too. For instance, i'll be stocking up on toilet paper at Costco this week - 10.78 for 40 rolls of Kleenex triple velvet

Or 779 for a Samsung 50" Smart LED TV - inc 5 year warranty (most costco electronics have a 5 year warranty). 20% off bausch and lomb contact lens solutions (my wife always stocks up on this). Half price (5.26 for 6 boxes) kleenex balsam regular tissues - will be stocking up on this for winter. Another thing I forgot to mention - you will pay a 25 pound per year fee to be a member of Costco - but you will make this back easily - even just by changing your car tyres which are typically very keenly priced. Booker is Free.
A trip to costco can be a family affair too - at Christmas they sell toys (well, from September they start) - they sell tools, automotive items, sporting items, books, etc. They have a little restaurant where they sell pizza, hotdogs, muffins, baked potatoes with toppings - VERY inexpensively - and soft drinks are bottomless - all you can drink. I think the baked potato with 1 or to toppings is 1.20 - pizza is 1.35 a slice (and it is a huge American sized slice), or a whole pizza is about 9 pounds - it is about 2 feet across. They sell their pizzas uncooked on an aluminum tray too - just pop them in the oven. Great for parties.
They do birthday cakes too - huge things, and they personalize it for free (I think it is free). The baked goods department is excellent - huge trays of fresh croissants, pan-Au-chocolate, bagels, and you can buy those par-cooked baguettes & chabattas which come in a protective atmosphere so they don't go bad until you open them and finish cooking.
As I said, you would have to be a pretty sick individual not to walk into Costco and not spend a couple of hundred quid
