When I was in grade school, mom gave me 25 cents for lunch money. With it I bought two hamburgers at ten cents each and a coke for a nickle. Food was not taxed. On occasions I bought just one hamburger, which gave me ten cents to buy candy at the Sundry Shoppe on the way home from school.
Shows how times have changed.
Anyway, $20 is way too much for lunch. Even at today's inflated prices you can get a burger, fries, and a coke for $10 or so. For example "The new $6 King Box includes your choice of a Burger King entree, a small order of fries, small drink, and two chocolate chip cookies."
I have to believe that $20 is both your allowance and lunch money.