I also add sultanas when I make up my own coleslaw. I make it simply with onions, white cabbage and carrot and mayonnaise. Put in pyrex bowl and kept covered in 'fridge -usually make enough for about three days use.
I have a salad most evenings as the main part of my supper/tea, and find the small containers of coleslaw can just about be spread out over a weeks usage.
I do not find the 3for2, etc offers annoying. Not for me as I live by myself and only have a small freezer, but so useful families, and must help a little bit for them.
I know the price of virtually everything I normally purchase 'as part of my weekly shop. Only ever buy 'special offers' if they are things I would normally purchase and then will purchase extra, provided I can store them. So things that do not need freezing or refrigeration I will purchase when on offer. (eg: the green tea I use is sometimes on offer and I will then purchase several packs to put away).
As I live alone, I do not find that food is a difficult part of my weekly expenditure. I buy mostly fresh food and cook from scratch. Reckon that I spend approximately £5 per day for three good meals.