Here are a few ideas:
Gamble - only if you're over 18. Odds aren't great, and it could be illegal (unless you're in Nevada).
Sell something: if you have a garage full of stuff, post things on craigslist for insane prices...tell them you HAVE to sell before 5 pm or something. Yes, you'll have to sell for way less than things are worth, but, it could work.
Similar, find a few odd jobs you can do (the more gross the better) in your neighborhood...somebody probably doesn't like to get their hands dirty and that's YOUR opportunity.
Gather up a collection of the nastiest bugs you can find. Setup a video clip of you eating them, with the option to pay to see you eat specific ones...you'll need paypal or similar (or if you have a crowd, you can do this in person)...so if you get paid via paypal, you might need to wait a few days to get the money, but, you'll have earned it before the day's done.
you can go for forex trading. as in this also we can double our money very soon.