Well when people talk proper angel investing it's all stocks and shares and silicon valley etc, but I think the general idea is scale-able.

So, I don't know: If you go with multiple small amounts then your own time deciding who to help will increase, so you probably don't want to deal in too-large amounts because the risk of the cash going poof will be high.
But $50 could buy someone a metaphorical fishing rod. Or, say, $500 could help someone buy ingredients, baking stuff and fancy packaging so they can start their international fudge delivery service. OR say, go up a notch and help someone revamp their cafe to include disabled access and a gamer's corner for local table toppers. And in return you could get some % of the resulting fish, or fudge, but hopefully hard cash profits ever after, without having to be directly involved in any day-to-day running of anything.

You will want a handy accountant and possibly a solicitor if you're dealing in amounts you'd really rather not say goodbye to forever, of course, and that cost would have to itself be accounted for. :)

(general disclaimer of knowing nothing applies.)