I pretty much cook everything from scratch, no ready meals and generally I dont buy crisps, sweets or fizzy drinks. I buy fresh ingredients and spend a few hours once a week making up big batches of food and then divide up into portions and freeze. I also make a lot of soup, its great for lunches and generally doesnt cost much to make.
Saves me a fortune at work as some folk I work with never cook and constantly buy ready meals and takeaways, easily spending £5 or more a day on crap food.
I've never actually added up exactly what i spend but its no more than £100 for the month and I eat really nice meals.