If you know some statistics / econometrics, then you could look into working with crypto data. The advantage is that most exchanges offer you free tick-data subscriptions as well as historical data. E.g. can you predict the 💩 coin ABC price in 5/15/30 min. based on some features that you design? Apart from working with the data itself, you also learn a bit about the infrastructure aspects (connectivity, persistence, ...). If you want to work with options data - Deribit has websocket connectivity and you could e.g. visualize and fit the live implied volatility smiles. Both projects will look good on your resume when applying to trading firms.