When my people are preparing a meal, how much food do they use? If they ever have anything less than 200 foods, I buy more. I stick to Groceries-Grains. Is this ok, or should I buy organic? How much food to they use in a day?

Thanks.

If it's the same as in the first game, food is used up not when making the meal, but when someone eats from the meal. It's a number like 10 or 20; not sure the exact number. I think that they can probably get by on grains, but they'll live longer if you buy a variety/organic.
They do use up food when you're not playing as far as I'm aware, but I don't know how much exactly. It would be wise to restock before turning off for the night (or if you're going to be away for more than a few hours). As long as they have several hundred food (I like to keep it over a thousand), they should be fine overnight.

The fridge has different visual states. When it's very full, there's some stuff on the counter. When it's partly full, there are bottles on top of the refrigerator. When it's fairly empty, then it's just plain fridge, no bottles or counter items.

I've found that if I fill the fridge to the bottle level, my people are fine overnight. Of course, this is a family of four; if you have six children, things might be different.