I've been reading Rich Dad, Poor Dad lately and his strategy seems to be pretty real estate heavy, or at least skewed towards more tangible assets than stocks or bonds. I like the idea of something that sends me a guaranteed (enter discussion on tenants) paycheck for as long as I own it.
Additionally, if you have considered these kinds of assets for your strategy, what kinds of things are out there aside from rentals or owning a business?
Welcome to the board, ND, I'm a little late to the discussion.
You've pretty much covered the asset allocation choices, and the key is to diversify among them. As long as you're getting an active-duty paycheck then you can afford to be aggressive with equities... small-cap value and international/emerging markets as well as dividend stock funds. No need to worry about bonds or big emergency funds.
Your challenge is to make sure the alternative assets fit your current lifestyle with current income instead of hoping for appreciation. For example rental properties sound great, but while you're on active duty you're almost never able to personally manage them. When you're deployed you're essentially turning everything over to a property manager (which eats up your profits) and hoping things aren't too bad when you return. The property appreciates at about the long-term rate of inflation (with wild variance by location) but the structure on it will consume plenty of maintenance, repair, and refurbishing money.
Kiyosaki used to write about more exotic investments like tax liens. The issue is that the further you go out on the alternative investment curve, the less liquid things tend to be and the higher their maintenance/transaction costs.
Maybe you'll do better with high-yield options like peer-to-peer lending or funding a real-estate property flipper, but again you have to consider what happens if there's a crisis in P2P while you're on deployment without bandwidth. Short-term high-interest loans to property flippers at least offer a lien on the property, but again it may be illiquid with high maint/transaction costs.
When you're no longer on active duty and have the time to be a hands-on manager, then the profits really start to flow to you (instead of to managers). But that's like running a business.
The biggest advantages to your current situation are a relatively high savings rate along with tax-favored investing in the TSP & your Roth IRA. Max out your contributions and let them compound while you're busy maximizing your flight hours. Read all you can about investing and real estate (and whatever else interests you) to get ready for the day when you actually have the time to do something about it. Take accounting & business classes so that you can learn all the various ways to make investments look more attractive than they actually are. Read all you can about the history of failed investments so that you develop a healthy streak of cynicism to go with your optimism.
The only other passive income option that I can think about would be blogging and eBooks. The first qualification is that you have to be a writer-- I mean someone who can't stop writing and really needs a focus for their output. Pick a topic that you're passionate about and start writing. It doesn't have to be more than a post or two a week at first (until you build up content for people to find via search engines) and then you may be able to tail off to a few times a month. If you can expand into podcasts and videos on your subject (especially helmet cameras!) then so much the better. Run advertising and affiliate sales on the blog, publish the eBooks as a download, and let the money start to trickle in. 2-3 years later it'll grow to at least a Roth IRA contribution and maybe more. The current 800-pound gorilla in this field is Pat Flynn of SmartPassiveIncome.com. A servicemember who's emulating Pat's methods is Mike at LiveTheNewEconomy.com, and you can watch as he learns.
However the writing/blogging idea is probably in the category of owning a business. It's a way to generate cash from a hobby that you'd be pursuing anyway. Blogging just allows for much more automation and passive income.
If you take anything from his book, let it be this...
