Cry and run out.
nothing, you just walk out without buying anything and leave the cart for the cashier
I might turn red but I wont run,
it could happen to any of us
Someone has to take those things in the basket and restock them. They won't just give you the groceries & stuff.
I pay with cash is what I do.
Tell them 'oh sorry i'm such a dumbass, I assumed I had money, looks like i'm one of them idiots'
Nothing. You leave empty handed. Although I'm not sure why you would go shopping without any money.
You can always call to check your balance. No matter what card you are using.