In the past, large affiliates were the mainstay, as catch-all coupon and media sites gave traffic to hundreds or thousands of advertisers. This is not so much the case anymore. With consumers using long-tail keywords and searching for very specific products and services, influencers can leverage their hyper-focused niche for affiliate marketing success. Influencers may not send advertisers huge amounts of traffic, but the audience they do send is credible, targeted, and has higher conversion rates. 
These ways of making extra money cover a wide range in terms of compensation and prestige. Check out the options to see what could work for you, keeping tabs on a projected per-hour rate so you can see what would be worth your time. The list is loosely arranged by 1. jobs requiring more skill or expertise, 2. gigs needing less and 3. things you can sell. And if you think of any good options I missed, please let me know in the comments.