The items in UT2004 falls into three categories concerning their respawn times:

• 82s (~3 x 27.5s) - It is really 82 seconds (because the exact time is actually 3 x 27.27s getting rounded down, but in other examples it will get rounded up).
  • Damage Amplifier (UDamagePack class) - item that doubles your weapon damage
• 55s (2 x 27.5s)
  • 100 Armor (SuperShieldPack class)
  • 100 health (SuperHealthPack class)
• 27.5s (1 x 27.5s)
  • 50 Armor (ShieldPack class)
  • Adrenaline (AdrenalinePickup class)
  • Ammunition (AmmoPickup classes)
  • Health (HealthPack and MiniHealthPack classes)
  • Weapons (Weapon pickup classes)

More (gamer) info about UT2004 timing here UT: The power of timing.