My OH was initially like this... We came to a compromise by working out what food items we could and couldn't bare to downshift on, and ensuring there was enough leeway in the budget for my expensive Evian habit, and his ability to eat a months worth of cereal in less than two weeks.
It's still made an enormous difference to our food shop, plus we don't have to compromise on the small amount of things that we do genuinely prefer to buy branded. To save money I stock up on things we prefer branded when on offer. It involved quite a bit of experimentation to start with, and does require a bit of forward planning and stock control... Plus I do an awful lot of comparing toilet roll prices per 100 sheets, and working out if bigger packs truly are cheaper or indeed sneakily more expensive per individual item, it's become a bit of an obsession if I'm truthful!
Once you get going though it's generally easy going, and prevents those horrific "bugger the toothpaste has run out and it's a Sunday night, and I'm working long day shifts all week" moments. My OH is so used to it now he becomes almost panicky when he discovers there are less than 3 varieties of cereal for him to decimate before the next batch magics it's way into the cupboards.
For example:
Heinz/HP reduced salt and sugar ketchup and brown sauce - usually £2.15 ish each in supermarkets... Always buy them when they're 2 for £3ish if possible.
Kellogg's cereals - just stocked up on 6 boxes of Coco Pops, Frosties etc for £10, usually around £3 per box.
cushelle toilet rolls - buy in packs of 24 from local £stretcher for around £7
certain branded cleaning products and toiletries due to my severe allergies - bought 3 sanex body washes for £5, normally about £3 each.
twinings tea bags because I personally think they taste far better - box of 240 are £3.79 in my local £stretcher, they are about £7.50-£8 in Tesco etc.