Focus on the surveys and offers at the top of the list. Here's a tip not many people know. CashCrate has a special algorithm that automatically selects the best surveys and offers and places them at the top of the list. There are several factors that go into determining which are the “best”, including payout, approval rate, and a variety of other factors. But all you need to know is that these surveys and offers are great, so you can do them in confidence!
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.
Drive for Uber or Lyft: If you're in a locale where you can find Uber or Lyft (or even one of the many competitors around the world such as China's Didi), you could easily make a respectable income. The hours are flexible and you can work as you see fit, making it perfect even if you currently have full-time employment but are looking to make some money on the side. 
Robert said he did an average of 4-6 of these gigs per year for a while depending on his schedule and the work involved. The best part is, he charged a flat rate that usually worked out to around $100 per hour. And remember, this was pay he was earning to advise people on the best ways to use social media tools like Facebook and Pinterest to grow their brands.