San Francisco is an extreme example of a place in California with both a large population (829,072) and high per capita income ($49,986). In fact, it has the highest per capita income of all places in California with a population of over 100,000. Though Sunnyvale ($48,203), San Mateo ($46,782), Thousand Oaks ($46,231), and Carlsbad ($44,305) join San Francisco to make up the top five places in California with the highest per capita income in that population class, none of them have populations even close to San Francisco. The next place with a population similar to that of San Francisco that appears in the per capita income rankings is San Jose ($34,992), and at this point, the difference in per capita income with the entire state of California is only about $5,000.
If you have an empty house or room you can rent it out on AIRBNB and OYO Rooms. Many travelers are looking to spend one night at a place. You can always rent out your empty house or room to them. All you need to do is list your room or house online, explain the rules and you are good to go. Travelers will pay you online. This way you don’t have to search for clients. They will come to you.
Portfolio income can come from multiple sources – interest/bond coupons, stock dividends, financial strategies including derivatives and capital growth.  Each offers some cash flow and some also offer potential capital gain with some risk from liquidity and volatile prices.  In this low-yield environment, many investors rely too heavily on cash flows and to pursue this are venturing further into riskier areas than they’d normally consider.