Use the middle seat belt, passed through the shopping bag handles, to keep the bags from rolling around and your purchases spilling out.
Step 1: Pull the Belt Out
A lot of cars have a middle seat belt that retracts into the rear pillar. On a hatch back this can be used for keeping your shopping tidy.
Step one is to pull out the belt.
Step 2: Loop the Belt Through the Bags' Handles
Step 3: Pass the Buckle Through the Guide
Step 4: Retract Any Slack and You're Done!!