It is interesting what your first reactive thought to this question is. Immediately he number $10 million popped into my head.
It is an amount I have considered could provide sufficiently for the remainder of my natural life. It would allow probably to buy a house and 2 or 3 cars (at different points in time as required not all at once). It would also allow a comfortable but not excessive life where I can pursue interests I choose whether for financial gain or not.