That Pay Well
You can offer private tutoring services in math, physics, writing, etc. You can even teach English online to kids from foreign countries. I tutored calculus through university, which was one of my best side jobs at the time.
Pet sitting is similar to dog walking, but you take care of the pet in their home. A good option if you don’t want the responsibility of walking a dog but still want to help out and earn extra money.
Ridesharing services like Uber and Lyft are becoming increasingly popular. You can sign up to be a driver if you have a car and some free time. You can set your own hours and drive when it’s convenient.
Food delivery is another great option as a side hustle if you have a car.
Transcription jobs are great for those who prefer to work alone and can type efficiently. The faster (and more accurate) you type, the more money you can make.