What is an easy side hustle I could do for a little extra cash?

I’m trying to save up for this expensive modification for my bike and I want to prove to my parents that I can be financially responsible. I just want something to do over the rest of the summer holidays without getting a proper job. I’ve already thought about pressure washing houses and cars but I’m a bit sceptical of it because of fear of damaging other peoples property. What are your ideas?