Stocks, bonds, 401(k)s, annuities, etc. are great ways to earn passive income. If you're not financially savvy, you'll want to hire a financial advisor who'll help you choose the right investments for you. You may want to take a couple of finance classes to understand what your advisor is speaking about when he/she recommends an investment strategy. Done right, investments can pay off for years. 

This is the best post I’ve seen on passive income streams. I’m similar to you in that I worked in IBanking for a few years but wanted out. My approach is a little different, instead of starting with the CD’s, I’m trying to build up my net worth with riskier asset classes such as stocks and real estate to get the benefit of compounding. Then, as I approach my retirement year goal, I’ll start moving them into CD and bond ladders. In theory at least, it’s best to have the highest net worth just before retirement, then convert them to risk free passive income. You’re method is more patient and probably more practical than mine. I guess I’m willing to take more risks.
It’s like if you met someone for the first time and the first thing they ask you is if you’re interested in buying something from them. I’d much rather get to know somebody first, trust them, and then have them tell me what they might have to offer. Or better yet, be genuinely interested in what they’re doing, and ask them about it myself. This is the kind of philosophy that I use when promoting other people’s products.
However, when you lack the money, you need time. You'll need to invest the upfront time now in order to reap the benefits of automatic income later. It just doesn't happen overnight. So don't expect it to. However, you can do this without quitting your day job. All it takes is some sincere effort over a consistent period, and voila! But, to get there, you'll need to consistently burn the midnight oil or get up at the crack of dawn. Your choice.
It’s a (mostly) short term, higher risk, higher reward place to invest cash that has a low correlation with the stock market, but is far more passive than buying and managing properties, has more opportunity for diversification than private placements (minimums of 5-10K, rather than 100K), and most of the equity offerings (and all of the debt offerings) provide monthly or quarterly incomes. Unlike a REIT, you can choose exactly which projects you wish to invest in.
If you’re worried about launching a new product, and think you might need some feedback to make it really good, Flynn recommends “pre-selling” an idea — for instance, offering a limited number of spots or seats into, say, a course you create and giving the test group specialized attention so you can see how to improve the content. Once it’s revised (or, if it’s software, once all the bugs are removed), you could open it up to your whole audience.
Selling T-shirts and other apparel is a pretty saturated market but the tools to do it are easy to use, which makes it very quick and cheap to get going. If you’re creative enough, or tap into the zeitgeist properly, you can also have a runaway hit. Even if your first 19 T-shirts don’t sell more than a few copies, your 20th might make up for everything.
Focus on your primary passive income stream first. It's difficult to grow your passive income into multiple streams if you don't already have one, solid stream. Focus all of your efforts on that one project first and help it grow as productive as possible. Then, you can take the money you've made and lessons you've learned from this passive income stream and put them into others.
Creating passive income is the key to retiring, especially retiring early. If you want to retire early with the stock market you will have to save a huge amount of money, because that money has to last so long and retirement calculators depend on you using your investment to fund your life. With passive income you will have income coming in as long as you own the investment, without every eating away at the principle invested. Creating passive income may take more work than investing in the stock market, but I think it is well worth the extra effort!