Paper towel - We use microfibre clothes and tea towels now.
Butter - Swapped to Ocado's £2.55 spread and it's fine.
Diet Coke - OH and I have both vowed to give it up after our current stash runs out. Just feels like wasted money.
Loo Roll - Haven't given it up, but have downgraded to a cheaper brand and we are buying in bulk. I do notice the lesser quality but it seems like a small sacrifice.
Toilet/pipe unblocker - Hated paying £3+ for this but our pipes are constantly clogging. Picked up some soda crystals for under a quid and they've worked a treat and will last a lot longer than a single use bottle.
Cleaning supplies - I did an inventory of what's under the sink and we won't be buying any more until we use up what we have. Probably have a years worth!
Toiletries - I wrote up a list of what we use and have buying in stock when items are on offer.
Ready meals - Given up most of these except Quorn (see below).
Eggs - I either buy medium or mixed size cartons now. OH hasn't noticed.
Condiments - Stocked up on mayo, ketchup, etc at Lidl where they are literally 1/4 the price of mainstream brands.
Takeaways - We haven't had one for a few weeks now and haven't missed them as much as we thought we would
Weekly shop - We're trying the buy every 10 days instead of 7 stretch trick.
On my to-do list:
Laundry detergent - I love Surf and have struggled to find something cheaper I like.
Quorn - We still buy a lot of freezer items ('steak' pies, sausages, burgers). Haven't found anything similar for cheaper yet.