Going back in time can always be a financial jackpot, no need to daily check the stock market. Just make use of the knowledge you have. While 3 years (counting from now) would be too short to use the GameStop short squeeze or the stellar rise of Dogecoin due to Elon Musks tweets (both earlier 2021, although Dogecoin has recently experienced another surge, quadrupling in value since summer) even a Japanese high-schooler moderately knowledgable about the happenings on the planet should have a rough knowledge about things like the russian-ucrainian war and its economical consequences and be able to utilise them.
Bitcoins are also a safe bet most of the time.