Think of an some service apps and get them developed. The simpler the better. Cutting out the middleman can create self-running money machines.
Here's some ideas:
-People post pictures and pay a few cents to get them edited. You take a cut.
-People post homework questions and pay ETH for answers. You take a cut.
- Truth or dare that pays LTC for doing the dare or telling the truth. You take a cut. (could get dangerous lol)
Up front cost for an mvp is a few BTC. Not bad for passive income.