> I know affiliate marketing is a big thing, but I generally never had enough of an audience online to make anything

You would be surprised how much you can make even without a large audience when you find something that you really like, that you can honestly recommend, and that other people are willing to pay for.

We recommend things all the time to eachother in a friendly, enthusiastic way. 

Consider how often we get super enthused about something and want to tell all our friends. I can't count how many people I have gotten into Terry Pratchett books over the years, I even have a signed copy which I am super grateful for because he passed away right afterwards (no connection, it wasn't my fault). The only difference is we share our enthusiasm and use a special link rather than a plain one.

Over black friday one of the pieces of software I use was offering a lifetime deal, I could have told people about it and made, get this, $700 per sale. I didn't because the market for that software is stupidly niche and I had other things to talk about instead, but just one person buying would have made $700 for software I could legitimately and confidently recommend? 

You're a guitarist, drummer and runner, that is a ton of stuff that you know about that other people want to get into and don't know the right stuff to buy or avoid, and people WANT gift ideas - Christmas present season is here!