Tbh I wouldn't same I can think of any proper 'hacks' but there are loads of things I buy own brand or even value brand that are just as good as branded versions. Shop Well for Less and the old Eat Well for Less proves that usually people cannot tell the difference between their usual brands and super cheap stuff.
Stuff I usually buy as cheap as possible that is just as good as more expensive stuff include a lot of my basic cleaning stuff (bleach, antibac sprays, antibac wipes, glass cleaners, cloths, scouring sponges, washing up liquid), lots of basic tinned things (baked beans, tinned spaghetti, tinned tomatoes, tinned pulses, tinned peas & carrots etc).
Superdrug are great for cheap own brand toiletries and cosmetics in particular. I use their anti-dandruff shampoo now instead of Head & Shoulders, it's just as good but a lot cheaper (and has the same active ingredient of zinc pyrithione to keep dandruff/scalp eczema at bay so works the same in that respect). I also use their super cheap vitamin E eye cream.
Sainsbury's baby lotion is a great simple moisturiser that is super cheap.
Always buy generic versions of over the counter medication where available as they are all the same active ingredients as the branded ones so unless you have a specific allergy or intolerance to something in a particular generic version there is really no reason to spend more. So paracetamol, ibuprofen, decongestant tablets, multivitamins, codeiene, hayfever tablets, diarrhea tablets...
If you can get to a good market, fruit and veg is far, far cheaper there than supermarkets. And often lots of other things too like hair accessories, some cosmetics, some clothing (basics like leggings for example).