For us it was two simple information radiators: the shopping list on the fridge and the weekly meal plan hung up nearby. Once a child could write, if they used something up they had to write it on the shopping list. If they wanted something we didn't have, they had to write it on the shopping list and we generally bought it. Yes, this resulted in some adorably written requests for MASHMLLS or CHKLIT, some of which we granted. Visiting children were also taught that when stuff was used up it has to go on the list. And we allowed our children, and visitors, to prepare food with an appropriate level of supervision.
It's simple enough, when you're making the meal plan and having trouble thinking up 7 meals, to ask the kids what we haven't eaten lately that they would like, and to put that on the meal plan and then add the items to the list. These two things will have them routinely engaged with the shopping list when they are at home.
In the store, they can perhaps push the cart (badly pushed carts frustrate parents and other shoppers, so make this a privilege that is easily revoked) and definitely get things from the shelves for you. We need canned tomatoes, get me 4 cans. No, that's not our brand, the one to the right of it. (For a young enough child, this is great for practicing counting, left and right, colours etc.) Hm, this size of the oil is 3.99 and this size is 5.99 and if you look at these tiny numbers on the sticker you can see that the larger size is a better buy. Let's get the large one. This label means the soup we like is on sale. We're going to buy more than usual because it's cheaper today. We need some sweet peppers. That one is wrinkly, don't buy a wrinkly pepper. We need apples. What kind of apple should we get this week? We need avocados. Make sure they are not rock hard. We need some meat. Wow, $11 for one steak? We can't afford that. Maybe we can afford the pork chops. I could buy this blade roast and pot-roast it, we like pot roast right? It's less than half the price of the sirloin roast. We don't buy chicken here sweetie, they inject salt water in it and I don't like how the chickens are treated. We can get chicken at the farm this weekend when we get the vegetables. There is already sweet cereal at home and it's not on the list, so I'm not getting that. Yes I know you wrote marshmallows on the list again, but they are a once in a while treat, not every week, so I'm not getting them. Hey! I saw that! Do you really like tuna that much? Don't put soft stuff down in the bottom of the cart, your brother might put a can on it and we don't want to squish it do we? I'll put it up here. How many bananas do you think we need for a week? Remember there's no school on Friday so everyone will be home for lunch.
Yes, it takes a LOT longer. But it's an apprenticeship. My kids are great cooks. One was able to be vegan (which requires a lot of attention to detail and willingness to cook for yourself) for extended periods of time and one is a chef (went to culinary school, works in restaurants and catering.) One of the visitors even followed those footsteps, also went to culinary school, and also works cooking.