I'm not sure this counts as a "hustle", but I manage all our household expenses and purchases. Between rewards on credit cards, ebates, and local store programs, I average about 1200$/year in cash back. We don't spend much - I mostly manage to stack up 3-4 rewards programs and rebates for every purchase, and then add coupons and online rebates. So, say I need pharmacy things. I'll wait for a coupon day at the pharmacy (nothing less than 30% cash back) and do all my shopping online then. Then I'll get cash back on the credit card, cash back through ebates when applicable, and then add coupons for specific items if applicable. Overall, I'd say I spend maybe 1-2 hours a month total coordinating our household expenses (in 5-minute shots - none of these tricks take more time than scrolling through email slush folders for coupons or clicking through a link), which means I'm averaging returns of 50$/hour, tax-free. Easy money. :)
Note: in the total above, I don't count the money "saved" by sale shopping, because I buy things at the price I'm willing to pay for them, and it's still money out of my bank account when I buy a thing, so I'm not "saving" money, just spending less. The 1200$ figure is the money back I actually saw come back (500$ from one credit card, 250$ from another credit card, 100$ from Costco, 225$ from a pharmacy rewards program, and the rest from ebates and a few other "minor" places.)
I'm starting a few other minor side-hustles, but they're not profitable yet (though they are enjoyable), so we'll see which ones actually make money above minimum wage. ;)