I can only shop at Tesco and Asda as I'm half an hour away from Aldi/Lidl/farmfoods/Iceland etc.
I generally so a small shop at each, each week so just look for what's cheapest in each, and know for example, that shreddies go half price every 2 months and stock up then.
Non brands are orange juice, kitchen roll, squash, pasta, ketchup, oats, museli, rice, flour, tinned fruit, tea bags, butter, frozen veg, frozen chips.
Branded but always an offer somewhere- shreddies, shredded wheat, weetabix, loo rolls, washing powder, washing up liquid, coffee, soup, beans, mayo, tissues.