The Digivice 01 is what Taichi uses to control Zero in battle from the sea battle onwards. He can upload food, herbs and even past battles from his victory book *with hillarious concequences* he mainly uses it for battle commands and as a 'Digimon Analyser'

The 5 V-Tamer Tags
Tag of Earth (Red) is guarded by Lord Triceramon
Tag of Sea (Blue) is guarded by Lord Marine
Tag of Spirit (Purple) is guarded by Lord Vamdemon
Tag of Metal (Grey true colour unknown) guarded by MetalGreymon + SkullSatamon)
Tag of Sky (No Pic) guarded by Juriemon, Megadramon + Deathmon

Rei's Pendant happens to be a Digimental that has the power to evolve both Arkadimon + Zero (it does get used for both)