6 Car boot sales This is a part-time occupation that increases earnings and broadens horizons as you make sales and get to travel, says Emma Jones, author of Working 5 to 9: How to Start a Successful Business in your Spare Time, and founder of the website enterprisenation.com. "Consider selling specialist items and building a reputation for being the go-to person; offering your knowledge and expertise with the product can increase the price you're paid," she suggests.