Consulting and Coaching (not requiring certification) can both provide fast paths to cash, if you have skillsets that make that possible.
Ebay auctions and other online auction portals can also offer an opportunity if you have inventory on hand to sell.
Can you hold an estate sale? Do you have goods on hand that have value that you don't mind relinquishing to free up cash flow. (Garage sales don't make nearly as much money.)
Consignment is another opportunity and takes very little effort. (Note, this isn't Craig's List, they want it for free.)
The key here is to know how much money you need to make and for how long. There is a difference between what you'd need to do and the skillset you need to have for $10/hour vs. $200/hour. I've worked at both ends.
A site like this one allows you great flexibility while allowing you to charge what you deem appropriate, leads can be uneven and the best way to generate is to get active with questions and drive business from other sources, like social media, and online forums.
Knowing a bit more I can make more targeted recommendations. Coaching and consulting require the least amount of effort and offer great flexibility.