Payload Injector and RCM jig
If you are exploring homebrews, you will probably need a payload injector (i.e. the SX Gear for Nintendo Switch) to load the alternative operating systems (or custom firmware) like Hekate. Without the payload injector, you will need a PC to do the job.
Decent sized micro SD card
You will likely need a micro SD card of you plan to download loads of games from the Nintendo Switch eShop. I highly recommend a U3 Speed Class micro SD card like the Samsung EVO Plus 256GB or the Samsung EVO Select 256GB.
These U3 Speed Class micro SD cards aren’t as fast as the Switch’s internal storage (i.e. NAND flash) but they are the best ones available currently.