1) Private Tutoring:
One of the easiest and most rewarding ways to generate extra income. You don't have to be an expert in anything to tutor. You can teach simple math to small children if you want to. Alternatively, you can teach about a subject that relates to your job or field of expertise. As a last resort, you can give language lessons to foreign students.
2) Part Time Job:
You have already thought of that we know, but still we need to list it. It could be a part time similar to your full time job or something you have never done before. There are plenty of part time jobs that do not require any specific skills or knowledge. If you find a part time job within your field of expertise, then chances are that you will be paid better than doing something that is new to you. Just keep that in mind.
3) Freelance Work:
Another way to generate extra income. When compared to part time jobs, freelance provides more freedom and choices. The tricky part is that you need to be able to manage your marketing and relationships. Part time freelancing can lead to the launch of a small business if conducted properly. There is no harm in trying.
Consider starting a blog. Because writing can be boring and hard to follow up, you need to choose a topic for your blog that you are passionate about. It can be a hobby, something you are crazy about or just something you know very well. Blogging will not get you loads of money, but if you enjoy what you are writing about then why not get paid for it as well. Earning money from blogs can be easily accomplished by the use of affiliate marketing.
5) Car Advertising:
There are many advertising companies out there that will pay you money to put an Ad on your car. Sounds like a great way to earn cash without doing anything at all. Of course, your car will not look the way you like it the most, but if you are in need for extra cash then maybe the your car's appearance is not on top of your priorities.
6) Make Use of Your Hobby:
If you have a particular skill or you are very good at your hobby then it could be a source for income to you. For example, if you are very good in table tennis, you can train others and get paid in return. This can be fun and rewarding both at the same time.