Business salesmen have historically had an elevator pitch. An elevator pitch is a presentation you can give to someone in the span of an elevator ride. What about it your life? Could you give a quick presentation on the purpose of your life as a Christian or perhaps a quick gospel presentation? Perhaps you should consider what you are about and what the gospel is so that if you have that checkout moment while you wait for the cashier to finish ringing groceries. Here is a verse I would encourage you to learn. It is quick and to the point and can be spring board to develop a longer gospel.
John 3:36 He who believes in the Son has everlasting life; and he who does not believe the Son shall not see life, but the wrath of God abides on him.”
Quote the scripture to that person. Then ask if they know why God’s wrath abides on someone? Because they did not believe in Jesus Christ. Describe what the penalty for sin. A person who lies, steals, commits adultery, murders, disobeys father and mother, covets, uses God’s name, and doesn’t worship Him will receive the just penalty of your sin. But the one who believes in Christ will have everlasting life. The person who believes upon Jesus Christ that he died and rose again for sin. By this
Really you can use any scripture but this one is a great one to start on.