$100 can not make you overnight millioner unless you win the lottery for buying a lottery ticket for 3 dollars at the gas station, just saying, do not do it anyway even if there is a tiny chance.
Example 1 provides more opportunities and may lead you to a great wealth and succes.
First of all forget about the money ($100) for a minute and think what you can do without it.
Start with assets, what do you have, what are your skills, e.g. you are good at writing or painting, singing or sports etc. Figure out what you do best of all and proceed from there, if you start doing something in what you are proficient in, most likely you will succeed in it quickly.
Keep the money for possible expenses. If you are good at chess, start teaching kids the basics of playing or bring the board to the park and play a game for 1 buck with someone there. (A real example); in this case you might need to spend cash for buying chess.
You got the idea, chess is just an example of many possible. Ask yourself what am I good at ?
Example 2 is a fast way to double your cash.
Find the events in your city which generate a lot of passing traffic like sport games, concerts, festivals etc, then buy a pack of water $3-5 and sell a bottle for $1 dollar or even 50 cents. That will triple your profit even if you sell just a few bottles. The only disadvantage is it is seasonal.
Example 3 just came up in the mind.
Stand in a line for 2 hours to get a ticket for any sports game which sells out and resell it for twice more before the game. Baseball, hockey, football are the best practices. Just watch the local “ticket mafia”, it’s been a very good business for a long time already.
There are plenty of ideas to make money even without any investment just think about it and keep trying.