Can I answer "both"?
Because let's be honest, the
best food bargains out there are usually to be found late in the day with yellow stickers on them. So it's a mix of just-in-time and stocking up! Having a decent sized freezer really helps, and being flexible with meal planning; plus having three decent cooks in the household so there's usually someone available to cook properly
So an evening of yellow-sticker shopping will usually end with lots of stuff in the freezer plus a couple of things to meal-plan around the following day. On a good day we'll end up with as much shopping as we can reasonably carry for only a few quid
As to things I'd buy regularly, anything that can keep reasonably well - dry pulses, rice, etc - gets bought in bulk, and I've recently started using Amazon's subscribe and save service. So stuff like detergents, toilet roll, coffee beans, cat food etc. just arrives at my door every month or two!