If I am not sure what to talk about, I always talk about where things are with my therapist. So I'd start with, "I hardly missed you at all this week. I did not think about you much." We'd probably talk about why that was. I feel like, when things are going well, it can be important to talk about why things are going well, and what's going well, rather than always focusing on the negative.
I also feel like sometimes just going in without a pre-conceived plan can be the most useful thing to do, just follow a thread and see where it leads--rather than deciding on the destination and marching there, if you know what I mean.