How to Save Money on Food when you are in Quarantine

You can't.

Okay, that depends.
Are you a typical American who eats 40% of your meals out, and shops at the nearest grocery store?

If so, then cooking at home and shopping less frequently may help decrease your costs.

Are you someone who has a price book, shops at multiple stores to keep prices down, and generally eats at home?  Then you are going to spend more money.

I am suddenly feeding 4 people 3 meals and 2 snacks a day.
My kids aren't eating free lunch at school.
We are physical distancing, and trying to shop only every 10 days or so.  Husband has been the designated shopper.
We are shopping at only one store, so you pay whatever the cost is and get whatever is there.
We are getting all our fruits and veg in our local boxes, and we are using "add ons" more frequently (eggs, bread, beans, honey, jam), and this is more expensive.

Baking bread 2x a week and eating oatmeal for breakfast doesn't help much with that.

However, what has been helping a LITTLE:
oatmeal
homemade bread
soup for dinner at least 2x a week
beans and rice once or twice a week