"What would you say to someone who thinks they just have to be a good person to get to heaven?"
"You are not saved through good works; you are saved to do good works."
In the early days of my preaching ministry, I used to tell people, "Do you know that all the good people are going to hell and all the bad people are going to heaven?" And that really startled them! The Truth is you can't get to heaven based on your goodness. The Bible says that no matter how good we are, it looks like a dirty rag in God's sight (see Isaiah 64:6). The only good thing that you can do is to confess your sin and surrender to Jesus Christ, receiving Him as your Savior and Lord and receiving His forgiveness. That way, God looks at you through the prism of Christ. He sees the perfection of Christ and forgives you.
Only receiving Christ's forgiveness will get you to heaven—not your hard work, not your effort. And once you come to Christ, the Bible says you are "created in Christ Jesus to do good works" (Ephesians 2:10). So you are not saved through good works; you are saved to do good works.