For a website the only best way to earn a passive income is the placing of ad banners from different ad networks on it. With ads banners only you won't earn much money, use short link service like that ad-fly. Affiliates won't give you money if you are the site owner, it's only interesting for the site users.
And for companies to give you money for posted banners your site should be very interesting. And it should be a lot of funky visitors. And this is very difficult to achieve. It takes a lot of time and effort to make the site interesting