Chew biscuit is another term for a dip or
pinch of chewing tobacco.
In other terms, a 'biscuit' is the shortened term for a dip.
The 'biscuit' or chew goes into the lower or
upper lip of the mouth which is also known as the 'basket'.
Example: "Hey man, wanna have a chew biscuit with me?"
"I could really go for a biscuit
right now."
Example: "I'm just throwing a biscuit in
the basket" meaning that you are throwing a dip of
chewing tobacco into your lip.