Reminisce about when you were a kid and things you did then. Tell them things you didn't when you were a kid, things that happened at school, or things you did with friends, etc. Ask about other family members or their old friends, etc. Ask your mom how to make that comfort food that you've tried and can't get quite right. It doesn't need to be deep, they just want to spend time with their kid, whom they love, before they die.
You have stories, everyone does, and so do they. Tell them yours and that might prompt them to tell theirs.