In a truck, boxes are good. I think a mix of hard and soft is better. For a car, SUV, airplane, etc. I prefer a soft bag. It fits into odd spaces better. For the most part I like several that are the same size, with smaller ones that will fit in the corners. Rectangular ones like the GI parachute bag are great. Surplus store ones are usually cheap but not very good quality. Places like GoRuck make excellent ones, but they are pricey. A box or two of about the same size is good for fragile items. I use Rubbermaid totes. A box and two or three kit bags will fit across the seat of a car and leave a flat surface for larger items. The trunk fills best with a few large ones and some smaller ones.

Respectfully,

Jerry