How come I vaccumed and cleaned out my car so I can take my nieces and sister to go shopping but the next day there's chip bags and crumbs everywhere again?

You should have foreseen the chip crumbs and not have bothered vacuuming the car.

Did you tell them not to eat in your car?  IF not then it should have been expected.  

lesson learned? vacuum and clean after the kids,  

LOL story of a parents life :-/

Because they felt like it.

Make them get really hungry, like starving and then have them eat the crumbs for you.

cause you let them eat chips in your car