The context of the following conversation is Casey was 75% full in the tank, but Casey bought gas anyway.:
Casey says I got an extra gas canister in the back seat..
The friend responds Why do you take extra gas with you?.
Casey responds Gas prices are much lower in Binghamton compared to Buffalo so I wanted to get what I could before we left..
The friend responds How much gas do you have now?.
Casey responds The tank is at 75% so I am good. It will likely take all of it to get to Buffalo and hopefully the extra gas will get us back..
The friend responds Well, if not, you will have to buy the gas for the way back..