Old Gas

I have a car that had sat for 13 years in indoor storage and the gas tank is like half full. (Amazingly the gas gauge still works too. )

the car starts and runs ok but obviously needs a tune up , I am a little concerned with the gas.

Should I try to pump it out or drain it and get rid of it

OR

Should I just burn it off since the car starts and actually runs on this old gas.

I have the storage receipts so 2003 is the newest this gas possibly is.