The following items are become unlocked when you reach the indicated level.
Great Ball:
Reach Level 12
Hyper Potion:
Reach Reach Level 15
Max Potion:
Reach Reach Level 25
Max Revive:
Reach Reach Level 30
Potion:
Reach Reach Level 05
Razz Berry:
Reach Reach Level 08
Revive:
Reach Reach Level 05
Super Potion:
Reach Reach Level 10
Ultra Ball:
Reach Reach Level 20