Domain names cannot be replicated. If one is taken, the only recourse would be to approach the owner to discuss a sale. While there are other variations you could choose, sometimes owning a certain domain (especially if it is attached to your business) can be worth the premium. Often, people will scout out domain names that are still available, buy them, and then sit on them in order to sell them down the road. Depending on who may want the domain down the road, you could sell it for a large markup.
The most liquid of the private investments are investing in equity or credit hedge funds, real estate funds, and private company funds. There will usually be 6 month – 3 year lockup periods. The least liquid of the private investments are when you invest directly into private companies yourself. You might not be able to get your money out for 5-10 years, depending on the success of the company and upcoming liquidity events.
I've got a $185,000 CD generating 3% interest coming due. Although the return is low, it's guaranteed. The CD gave me the confidence to invest more aggressively in risk over the years. My online interest income has come down since I aggressively deployed some capital at the beginning of the year and again during the February market correction. You'll see these figures in my quarterly investment-income update.
The theoretical generalization to more than one period is a multi-period wealth and income constraint. For example, the same person can gain more productive skills or acquire more productive income-earning assets to earn a higher income. In the multi-period case, something might also happen to the economy beyond the control of the individual to reduce (or increase) the flow of income. Changing measured income and its relation to consumption over time might be modeled accordingly, such as in the permanent income hypothesis.
These days, low-risk bond yields aren’t enough to meet most income needs. When investing in bonds, the income typically comes as coupon payments – contractually guaranteed interest payments at predictable intervals.  There are many kinds of bond income available, so you must strike a balance between reaching for higher income (yield) and limiting risk.