Thats what the mr fusion is for. Remember Marty dont go too far back in time without a full tank of gas. The flux capicitor just initiates time travel you still need gas to drive the car. One of Docs flaws in his design.
I bet they put that in there for all the jerks ( like me) who have called asking for a flux capacitor.
Side note, I called autozone and asked for one and it was ordered under the name marty mcfly and she went and checked on it for me. Unfortunatly it looks like it was never ordered she said. Then asked me for the make and model of the car. I lost it after I told here it was a DMC DeLorean. Had to hang up. Not sure if she was just humoring me or she really was obvlivious.