I just simply take any trash out of the vehicle when I get out...home, work, gas station, car wash, etc. You likely walk by a trash can within 5 seconds of exiting your car virtually anywhere you may be. It stays pretty well spotless even with 4 kids. The center cubby under the hvac and the rear trays over the wheel wells in the back usually work fine for the random paper or wrappers from the current drive. We don't allow full fledged meals to happen in the car, ever. A quick vac every week or two gets the gravel bits and random crumbs.
A car that smells like any kind of old, stale food/trash is a sore spot for me. I've driven rust buckets I keep more clean than some 6 figure cars I've worked on in the past. We used to have a detailing business and it just became habit to have as clean a vehicle as possible at all times.
Now if I could just get the same cooperation from the kids in the house...
