Five Sources of Income for Retirement - what is the Fifth one ?

[Sachin Amin]

Hello BP community and for those who already made it :-) :-) (Baby boomers & Gen X)

when I was in school some one once said to me, to be financially free you need to have five sources of Incomes - at that time I was naïve and I translated that into having 5 Jobs :-). fast forward 20 yrs and that statement was stuck in my subconscious mind and as you know if something is stuck in your subconscious mind for a long period of time, your mind tries to achieve that goal with out you knowing it - basically it works out plan to achieve that goal(quote from Napoleon Hill's - Think and grow rich). most of these are aimed towards retirement or financial freedom -

so my question is what would be that ideal fifth source of income to add in portfolio :
I have :
1) a good paying job (W2 Income) - My first source of Income

2) a REI portfolio (anything & Everything related to REI) - My Second source of Income

3) a strong 401k Portfolio (401k -good company matching, IRA's , Social security etc.) - My third source of Income

4) a growing stock portfolio - My fourth source of Income

5) ??????????????? I need your help determining what would be that ultimate "Fifth" source of Income

I know many have figured these income streams - specially baby boomers (born between 1946 and 1964) and Gen X (born between 1965 and 80) and I as a Millennial requesting baby boomers and Gen X to advice as they are the one's who have laid down a strong foundation for us "millennials" so that we can do the same for Gen Z , Y.

Bring it on!!!!!

Cheers