I've got 'em all. Waitrose, Tesco, Nectar, Boots, Superdrug, Boots, Co-op, John Lewis, M&S, Matalan, Halfords, B&Q etc. I don't carry the physical cards with me, they don't cost anything and I store all those on the Stocard app on my phone so they are always with me.
I don't know why I'm holding out about the whole loyalty card, data sharing thing. But it still feels a bit uncomfortable. I know it's illogical, because it's unavoidable when I buy from Amazon etc.
At least this way I can benefit from Nectar Prices. I'm new to this, but the savings from Nectar Prices seem to dwarf the value of the loyalty points I would get if I registered it.