Buy and cook in bulk. Its generally much cheaper to buy big packs, multi packs, value packs.
Use the BOGOF offers but make sure you cook it all up and freeze what you don't use fresh. Make sure you freeze in appropriate portion sizes - i.e. don't freeze a pack of 12 sausages if you use/ typically cook in quantities of 6.
Bulk up meals with vegetables like cottage pie use half mince and half grated/ chopped veg.
Make base sauces that are multifunctional like a meat/ veg bolognese that you can portion freeze and then add to pasta, make up as a lasagne, top with mash for a cottage pie, layer up with potatos and top with a bit of cheese for a potato bake.
Buy big bags of potatos and always cook up double (or more) so you've got ready food in the freezer for days when its all a bit mad. Ideal for mash, parboil potatos for roasts, parboil for wedges (oven wedges), herby potatos like Parisienne.
Lots of big soups using up all left overs.
Freeze 1/2 bread loaf if you're not going to use the whole loaf - if you slice it first you can toast straight from the freezer.
If bread dries out then bag it and use it as breadcrumbs/ freeze for later use.
Biggest thing is don't throw anything away. Plan how you are going to use all your ingredients when your fridge/ cupboards are full.
I don't live near a supermarket so have to be very organised in my shopping hence my love of the freezer.