List of UNSC crates
From Halopedia, the Halo wiki
Summary
Scattered throughout multiplayer and campaign levels on Halo 2 are UNSC crates, or large boxes, that contain supplies for ground based Marine forces. The contents of crates can be identified by their labels, and range from portable generators to armored boots. Although their only actual use in the game is cover from enemy fire, they do reveal a bit about the UNSC military.
Crates
There is a range of different types of crates. This section contains information on all of them, ranging from smallest to largest.
Kits
Rescue
The first crate can be found only once or twice in the game; it appears to be a small medical kit Marine medics would use to treat the wounded. It has the word "Rescue" along with the internation medical symbol. It is likely able to be found in various campaign levels at Marine positions, but it can only be found once in multiplayer on the map Foundation.
Nerve Gas
The only place this crate has been spotted is on the multiplayer map Foundation. Perhaps it is with a bit of dry humor that Bungie placed this small crate right next to a medical kit within the same room.
Type: VX 7
Barrels
Barrels contain liquid supplies.
Water
This crate (or barrel) can be found all over on multiplayer maps and Marine encampments in campaign. It appears to be a barrel of water for hygiene, cleansing, drinking, etc.
Type: Pure
Hydrogen
It's likely this is used by Marine ground forces to fuel various equipment, including generators and Warthogs.
Type: Fuel
Small Crates
These crates are smaller ones that generally contain infantry equipment.
Gas Mask
Gas masks are used by ground forces for protection against chemical or biological weapons.
Serial Number: 7880-53-413-1990 Type: S90 Item: Gas Mask/KR3/INF/BLK Quantity: 64 Weight: 112 LBS Lot: LYSE7Q409-53