We're under £100 per week as well (central London, two adults & three children).
I do a big shop at Lidl every three or four weeks, which comes to about £90 a time, with occasional forays to wholefood shop or Sainsbury's for more specialised things (no more than £10 per week). Most Lidl stuff is pretty good quality, I find, you quickly learn to avoid the few duff lines. It's very hard to spend more than £100 in Lidl, even if you do a massive stock-up on eg. Christmas/birthday things.
We have milk delivered (approx £10 per week) and I spend another £10-£15 in the greengrocer. Bread comes from the breadmaker, flour is included in the above. I usually buy a roast for Sunday lunch, up to about £10 unless it's a special occasion, but generally get three meals out of it, so seems like a bargain. I also stock up on meat at the farm shop near my parents in Devon, which is v. good value.
This week we have had/are having:
Sunday: Lamb joint with potatoes and cabbage
Monday: Spanish omelette with chorizo using the left-over potatoes and cabbage
Tuesday: Lamb casserole with chickpeas and couscous (leftover lamb from Sunday)
Wednesday: Roast vegetables (aubergine onion and courgette) with tomato and pasta
Thursday: Pizza (dough made in breadmaker) with the rest of the chorizo, and salad or broccoli
Friday: Haven't got that far yet, but will probably involve jacket potatoes, tuna and salad/broccoli (whichever we didn't have on Thursday).
This week is unusual in not having soup at some stage -- any kind of boned joint or chicken is almost invariably followed by casseroled leftovers two days later, and usually soup a couple of days after that. Other dishes I often make are: risotto, chilli con carne, pasta bake, sausage casserole, tuna rice and lasagne.
I did have a slow cooker for a while but never really used it -- I don't want to cook in the morning, and I never really worked out what the slow cooker could do for me that an oven couldn't.