I will put The Great Divorce on the list. I might reread Mere Christianity first; it’s probably been 25 years. Lewis was a great writer and thinker.
And if you want to be able to solidly answer atheists that say, “why would your loving god allow so many innocent people in the world to suffer”, you need to read “The problem of pain.” :)
Another Lewis gem that is a good read for our current age is That Hideous Strength. It’s the 3rd book of his (rather unusual) foray into science fiction, but filled with the usual Lewisian insight. In particular it depicts a scenario of an ascendant Hell working through its control of the intelligentsia in a way that echoes with what we see around us today.