I use these to lock any boxes or suitcases in place. Same as the Hyundai ones for 80% less. (Note, the link is for ones made for a vinyl cargo mat like i have, but they also have a version made for a carpeted cargo mat or no cargo mat.) They work great.
I also have a cargo net to stabilize grocery bags, and a have a four compartment storage thing that hangs off the back seat headrests hidden by my cargo cover.