Anything where I have a well-defined thing that I want, but I don't have the talent or expertise to do it myself. For me that's design work, but for you it could be setting up a database, creating a kernel module, etc. I view outsourcing as a way to save money in the long term, but good outsourcing should cost a lot up front. If you're looking to save money right now by outsourcing, you are probably going to get what you pay for.

Probably anything that needs Photoshop and any fronted design that I cant just use a bootstrap theme

I've been considering outsourcing the creation specific ReactJS (and react native) components where the interfaces/state can be defined by me.

Integration if you don't know the system you have to integrate with. Establish some sort of a protocol (simple example: passing xml data), ask what this other system needs as input. The rest of integration I'd outsource.