As a player, you could buy Roll Cages for your trucks.
Each Roll Cage could hold 8 - 12 boxes. You would have to load the Roll Cage first before putting it on the truck. Like a forklift, you should be able to drive the Roll Cage into a shelf or vehicle to load / unload items.
The benefit is instead of going into the store to grab a Handtruck, or taking up a slot in the truck storage with a Handtruck, you could pull out the Roll Cage and drive it straight into the store.