When I was single in southern Cal, I got breakfast and lunch from the food truck - were called "roach coaches" then, don't know about now
Never bought groceries.
They had healthy stuff (yogurt, fruit, cereal, salad) and not-so-healthy stuff if you were so inclined. They made the best turkey avocado melt ever.
In the 70's the couple who lived across the street from my grandmother quit their jobs and bought a food truck. then another and another...they made a fortune. Kept adding on to their house until it was a little McMansion in the middle of a normal, middle-class Atlanta suburb.