I am in the same boat OP and have a 12 year old. That eats a lot.
I have to go every other day. I have to see what fresh stuff is available and weigh up if I can carry orange juice and the 2 potatoes I choose/fish/strawberries/cans of tomatoes.
It is EVERY OTHER DAY!
I mean, toast, butter, eggs and juice, coffee for me, are minimum just for breakfast.
I goes on and on...
God forbid I want a bottle of wine.
Heartily sick of it and my back hurts, but what can you do? I feel your pain!
Also, you have to really, really plan. Every meal. Pasta, tin of toms, cheese, bla bla. Dinner, I'll cheat and get a pizza... it all weighs so much. Yogurts? Icecream on top? DD asked for a can of lemonade for a treat. I had to think twice and ditch a punnet of strawberries...