For types of walkie talkies make sure you get a PMR446 system, this relates to the frequencies used and this is open to the public with no licence required.
You can buy cheap or expensive, but make sure you get ones that support the standard 8 channels plus the 38 extra CTSS codes. These act as if they are extra channels, e.g. channel 1.00, 1.01 to 1.38, then 2s, 3s etc
Headsets are not essential but without a headset it will go off when you are sneaking up on someone.
So as above try to go for one with a common socket type
Turn of VOX - it is the spawn of the devil. With VOX it transmits when you speak so works handsfree.
Whats wrong with this is it is set of by heavy breathing, shooting etc. (And by HPA compressors!)
With PMR446 you can link up with other players at the event on your side.
Some events publish channels allocated to sides, or commanders will allocate channels / sub channels to teams.
Make sure you do not interfere with event staff if they are using PMR446
At NvS there are a lot of players and a lot of radio traffic. However the South took back the win due to very well organised communications.
Other than PMR446 the American FRS walkie talkie. (Family radio service) These crop up in the UK but are illegal as they are not in the correct frequencies (and can interfere with teh fire brigade)
Licenced frequencies are available, but are more expensive as you need the licence and to have the appropriate walkie talkies reprogrammed for you. These are a good option for team wanting private communications, and is the common type used by sites for running events.
Licenced systems can be hired
Dont forget if you want comms between your team you can use mobile phones.
I have done so, and even at NvS in the old venue I have sent for both paint and reinforcements by phone
This saved a position for the South (for a bit) when half the people in the safe zone were called into action!