What other thing do you invest in outside or real estate?

[Jack Ni]

It seems like most millionaires have multiple source of income, so I want to have multiple source of income as well (this way, I can sleep well at night hahaha) 

My first obvious source of income is obvious rental properties. Currently I have 2.

My second source income is Google Adsense. Making money off ads. 

My third source of income is selling private label products on Amazon. 

My fourth source of income is investing in the stock market. Buy and hold type of investor, usually holding more than 10 years. I also collect dividends from my stocks. 

Or this could be what other source of income do you have? Really curious to know