Know when (and when not) to use Viglinks and Skimlinks. If you applied to an affiliate program but were denied, you might be able to still be an affiliate for that advertiser through a secondary affiliate program like VigLink or Skimlinks. Basically, they themselves are affiliates and will split their affiliate commission with you if you put their affiliate link in your content for an advertiser. Obviously, the commission rate is lower for you in this case, so if you ever are accepted into the advertiser’s affiliate program directly, immediately switch from using VigLink / Skimlinks affiliate links to your own.
You can sell your ebooks through Amazon's Kindle program or Apple's iTunes Connect, which gives you access to a large majority of the digital-book reading market and the barriers for entry are incredibly low. You don't need to invest lots of money to make this happen, but you do need to invest lots of time, not only in writing the ebooks, but in marketing them as well.
If my piece of content is so unique and valuable around hiking backpack recommendations, that other reputable outdoor websites are willing to link to it and build the page’s authority, then I’d have a very real opportunity to rank high in organic search for these search terms (meaning, my page will come up first when someone searches for hiking backpacks).