Monetize a hobby. While some hobbies actually cost money, others can be transformed into a profitable business venture. Ultimately, it depends on what your hobby is and how talented you are. You could turn your love of photography, for example, into a part-time gig taking family portraits and wedding photos or selling prints on Etsy or at arts fairs.
Affiliate marketing is a big and profitable industry that covers a wide spectrum of topics and fields. If you have got an interest in fitness, you can make money promoting fitness videos or courses e.g. videos to loss your weight. In fashion wear, you can earn commissions by recommending friends to clothing or t-shirt of companies which are offering affiliate programs.