In the US, there's an invaluable resource we use when figuring out a reasonable grocery budget. The US Department of Agriculture (USDA) puts out a monthly report at https://www.fns.usda.gov/cnpp/usda-food-plans-cost-food-reports-monthly-reports which gives details estimates of food costs per person by age, gender, and gradation of spend level (Thrifty through to Liberal). I'd highly recommend it.

We also put basic toiletries and household goods you could find at the grocery store in that budget line item and found it's still a reasonable estimation.