Setting up road side stores that sell edibles like beef rolls (Gala is the most popular brand in Nigeria), tasty biscuits, chips, bottles of water, and more, can be a way to make quick money.
Hire a person to stay in a store beside a major road that usually experiences a lot of traffic. The population of thirsty and hungry people in the cars that drive by will help your products sell out faster.
Note:
This point does not in any way endorse street hawking. Avoid hawking at all cost. Having a decent store close to a majorly trafficked environment is a more modest way to earn an extra income.