There are no verses regarding grocery carts–the scriptures are silent on the subject. I act because it’s Jesus showing me the path I should walk today. In the course of a day there are seldom clear biblical mandates on the decisions we need to make. Of course over time there are some that apply, for example prohibitions against sexual immorality, divorce, and commands to love our neighbors. But when it comes to ordinary stuff: the financial decisions, what church to attend, the right course in disciplining our children we don't get explicit biblical direction.
It’s not through lack of trying. I know I spend time trying to understand the Bible–reading books, talking to people, meditating on scriptural passages. We want clarity, but God usually offers mystery. To cope with this mystery Christians invest large amounts of energy creating summaries of biblically supported truths. We generate creeds, confessions, statements of faith, core beliefs, doctrinal statements, etc. to codify what we believe is important. Typically these are heavily driven by scripture–but ultimately these are human creations–not the inspired word of God.
We look to the scriptures to tell us what is right and wrong, as we should. But do we look too much? No one argues with, “You shall love the Lord your God with all your heart and with all your soul and with all your might." That is clear. But not much else is free from debate. The Bible provides direction for living our lives, but it's an outline, not a spell checker. We want the Bible to be a rulebook, but more often what we need is a conversation with God.
P.S. When I got to the grocery store today, the parking lot was strewn with abandoned carts–at least eight. Was I supposed to roll in one or all of them? God has a sense of humor...