Lidl for chocolate, olives, tinned toms, veg (although it's a bit hit and miss and doesn't keep for long), olive oil, peanut butter, rice, pasta, beer (some good ones always seem to be on special offer), milk. Waitrose for the rest.
I think the quality of Lidl is fine from what I have bought, ours isn't that big so doesn't offer all the ranges, it is a bit like East Germany before the wall came down though!