I am going to walk out on my restaurant bill.
Why won't you pay for your food at the restaurant?
My credit card won't go through at the restaurant and I don't have any cash either.
It is your responsibility to make sure that you have the funds to pay for your food prior to ordering and consuming it. You need to make arrangements to pay the restaurant for the food that ate, as it is your obligation.
I am getting the hell out of there before they figure out I'm broke.
You made an agreement with the restaurant as soon as you ordered your food and bailing on your bill now abdicates your responsibility to compensate them for their services which is incorrect. Don't try to skip out or you will find yourself in jail for theft.