What I would do if I needed to make a $100 in a short period of time. And how my opportunities will change through the years.
If i needed to make a hundred dollars in a short period of time right now in 2019 I would start a local lawn care business and hire my friends to do the work. My plan would be to charge the customer 100% of the price then let my friends (employees) take 70% ,leave 10% to repair any damages, and I would keep 20% as manager and head of marketing + advertising. Then over time the 20% will start adding up and then I would soon have my $100.
In the coming years if i need to make a quick $100 I would probably just sell some junk thats laying around. A garage sale might be a good option. I would find the price that I payed for an object that now has no worth to me I would then find 75% of that price and list said object for 25% off. Thats what I would do if I needed to make some quick cash in the coming years.