A pair of 16oz gloves for sparring
A pair of bag gloves and/or some fingerless grappling gloves for pads and/or rolling
A pair of shin/instep guards
Some flexible shorts (fight shorts/board shorts)
Headgear and/or a body protector are more an issue of preference. Nice to have, in my opinion.
Things that're really nice to have, but not necessary...
Wrestling shoes (if that's how you roll)
As a rule of thumb if you buy cheap you buy twice. Higher priced gear is going to last longer and be of higher quality.
"I don't want them to like me, because when I'm in the ring, punches fly to the face. It is not a tenderness time. I am not falling in love. And he knows that when the fight starts I am kicking faces."
- Wanderlei Silva