Craigslist is a great place to find day labor under the table jobs like moving furniture, or painting a fence. Really any classified ad is a good place to start. There are day labors in every city just about, ask a homeless person where to find one if you are hurting for cash. Sometimes they will feed you in the process. But these are long hard hours, and you dont get paid enough for your hard work.
If you have nothing better to do with your life, cans and bottles will make you money. But while you are at it, pick up every penny you see on the sidewalk, pick up every scratched off lottery ticket and double check it, (sometimes drunk people scratch them off but cant figure out the rules and toss them not realizing they won) pick up cok3 caps, and sell them online, sell scrap metal, sell your time on craigslist, sell your soul on ekbay, sell the world to aliens on a cb radio, there are a million ways to make money, use your head.
There is always street performing. I saw a guy once holding a radio playing music, and lip singing to it, at the line for the Ellis island ferry. He was actually making money! This made me think. Technically you can just ask for money, but why not do something entertaining for it? Like read a book out loud. Since ive seen several street performers, and they all do something anyone can do (for the most part) so i think when i got some free time, ill give it a whirl. Although talking to some of them, in some areas they have to have city permits, otherwise they get slapped with hefty fines. (what kind of bull crap is that?)
my friend vegasjay rented a 70$ gorilla suit, and got tourists to take a picture with the gorilla for 5$ a pop, he banked on that one, and think about the naked cowboy, play guitar naked on roller skates, and people will pay you. Theres a million things you can do for cash.
which brings up another suggestion i heard today. If you can find a willing significant other, and a cheap ring (maybe from a thrift store or something) you can always propose as a scam to get things for free. People love lovers, especially newly weds, so take a knee whenever wherever, even get some resteraunt staff in on it, you might even get better seats at that event you have been wanting to go to.
While were on the subject of scams, you can also purchase (or dive depending) some military camo, then wear it, clean shaven and stroll around and see if you can pray off of peoples patritisim. The other day i really wanted to go to the top of the empire state buildinng, (for the elevator ride) but it was outrageously 18$ per person! At the bottom of the sign it said discount with military id, and free for men and women in uniform. So i went back the next day shaved, and in uniform, no joke i got escorted to the front of a 2 hour line, they didnt even check my id, and escorted directly up and down the buildinng. When i came down, i even got an elevator all to myself! It was fantastic! So keep that in mind