I think someone else mentioned it, but see if you can go along to the store when the family shopping is done. They might not be getting what you want because they forget or don't want to bother going out of their usual routine. Suggest that you'll pick the vegetables for the week and head to the freezer or produce aisle (which can be cheaper too depending on the season, and when you factor in how much water you're buying in the canned veggies.) If the cost is brought up, say it's MUCH cheaper than blood pressure, insulin, or heart medicines if you don't get your weight under control.
For 3 days, I get to part of a thousand other journeys.