Ask HN: I've 2m/m unique visitors, what to sell to them?

I have more than 2 million unique visitors on my sites (~10 sites) and I'm not selling any product to them. I'm earning money on other ways like selling links and promoting specific services (affiliate) but I really like to turn to product. So, I need your advice, thoughts and sharing experiences like this. My sites has to do with traveling and education.