We do this thread on the 'Food' section. I use Aldi for basics then pop over to sainsbos for the other stuff or branded stuff which is better.
I am one of those Waitrose bagged women too - just cos I reuse the bags and love waitrose!
However, I wouldnt say you save a vast amount. As I buy the premium side of the Aldi stuff your not going to save as much as you think. Some of it is rubbish and false economy. I buy the paramasan, premium tom, some breakfast cereal, everyday biscuits, veg, cream cheese, apple juice, nappies & wipes, washing powder, the better chocolate.
You need to meal plan before leaving the house, thinking about what days suit certain types of meals. I def believe its cheaper to batch cook, so eat one freeze one. Use cheaper, slow cook cuts too. Think about food waste too. I dont buy glossy magazines anymore, no crisps, readymades, pasties/sauage rolls (all cack). I buy what I need.
I cook from scratch and do loads of baking too. My weekly bill still comes in around £100. I was spending £140.