Merchandise is a cool way to get money, but there is kind of a lot that goes into it.
There are physical products and digital products.
For physical products, we've got things like hats, t-shirts, maybe mousepads.
You can have all these made and then shipped to you (upfront cost + hiring a designer), then sell and ship them yourself (now add in labor costs).
Or you can set up w/ a site like Society6 where you just upload the design and they handle everything.
The profit margin there is really really small though.
You'd have to sell a lot to make a living.
And you still probably need to hire a designer to design the merchandise.
Physical merchandise is tough but it's do-able.
I propose a better idea: digital merchandise!
The best example I have is to teach people how to play the games that you play.
You could do a video series or write a book if it works out that your subject doesn't really need to be seen.
For example, maybe you're good at StarCraft.
You could do a video series teaching people how to play each race well.
Then sell that as a video course. I recommend using Podia