What is the easiest thing to flip for profit?

I'm curious, what's the simplest item or asset to buy and quickly resell for a profit? Is it something like rare collectibles, stocks, or perhaps, in today's digital age, cryptocurrencies? Are there any particular strategies or factors to consider when looking to flip something for a quick return? And what about the risks involved? Is there a way to minimize them while still aiming for a profitable flip?