I somewhat accidentally discovered something that could potentially be called a side hustle, though I'd happily do it for no monetary reward... My employer pays a good chunk of change (over $1,000) for each employee referral you make who ultimately gets hired. So for a very low time investment on my part (usually a meet-up over drinks or coffee with someone from my network who I think is awesome both professionally and personally, and then submitting their resume into an online system), I make a little money!
Keep in mind that I have only done this when I think the candidate would be perfect for the role and would thrive in it. But when those conditions are met, of course I'd refer the person, referral bonus or not! The good news is: two of my referrals have gotten hired in the past few months. Both are thrilled with their new gigs, my company is thrilled to have landed them, and I'm thrilled to be a tiny bit closer to FI for something I would've done anyway :)