This would only require the investment of your time. Start with a blog on something you love. It could be anything. From a travel blog containing pictures of your travels to a sports blog dedicated to your favorite team/sport. You can blog about anything and everything. It doesn't matter. But write regularly! I've read that an online magazine editor would personally prefer someone who posts something daily over someone who writes long posts once or twice a week.
Most of us think of investment income as just the cash flow we get from bank interest, bonds, share dividends and property rents, some of which comes via a super pension.  But a more complete view is to also consider how growing the value of your investments can add to your spending potential.  This total return approach generates income from both income and growth to optimise spending from your portfolio across all market cycles, aligning cheap and expensive investments to your goals.