Camera, video transmitter, video receiver and something to see it all on like a screen or goggles. Power for all of it.
This is minimum.
Depending on where you are (what country) and what you fly (fixed wing or multirotor), there are lots of options.
I suggest you look at getting a camera and video transmitter (VTX) that run on the same voltage or where the VTX can power the camera to make the wiring simpler.
I like goggles because the experience is more immersive. I have a screen for recording and for flying FPV in places where I must be able to maintain line of sight (LOS). Some goggles have built in DVR. This is fantastic but best if you have something that can play video from an SDCard with you at the field.
Sit for your first FPV flight.
Record you flight and have some sort of buzzer available on your machine. Flying FPV is fun. Crashing happens a lot for me and for lots of us. When you crash, it can be amazingly hard to remember where. If you have a recording, play it back. Then trigger the buzzer and go find your model.
If your VTX output is RP-SMA, use an RP-SMA antenna. Yes, you can attach an SMA antenna to an RP-SMA VTX under the right circumstances. No, it won't work. It happens often enough to mention because the goggles antenna often looks the same but is the opposite. :black_eyed:
Do NOT power your VTX without the antenna firmly attached.
Don't forget to tune your camera. Default settings on an FPV camera are rarely the best for FPV flight. There are lots of instructions online (RotorRiot FGA does one) to help you. It is often simplest to do this before you install the camera into your model.
EDIT:
One more thing I'm sure you're gonna need. More props!
Happy flying!