The most obvious place to hide your cash is in a fireproof safe. Remember that not all safes are fireproof.
Cash and other valuables can be stored in fireproof bags.
Ceramic toilets frequently survive fires (porcelain). This material is heat resistant, therefore your cash will be safe within the tank.
Cash in your car only works if you live in a safe area and it is neatly disguised.
In your car
Your freezer is another favourite spot to stash cash. I'll store it in a chest freezer instead of a standard fridge.
In the freezer
While not as secure as the other options on the list, it is an option if you have a crevice or secure place in the garage to conceal the cash.
In the garage
Put your cash in a container and put it inside the burner.
Wood burning stove
The fireplace is fireproof since it is normally enclosed by metal or concrete.