Health pack
From Halopedia, the Halo wiki
Summary
On the battle field, Marines, and even Spartans need to have health packs, or MedKits, available. Each MedKit carries small stores of BioFoam (see below), stitch kit, sedatives, and bandages, and other useful field dressing components.
BioFoam is a healing, coagulant foam that is inserted into the skin and even deeper into the body itself. This foam keeps damaged organs in place and helps stop bleeding and hemorrhaging. It is, unfortunately, very painful to use.
These are only in the first Halo video game. In Halo 2, health regenerates on its own, much like the Master Chief's Shields
Images
http://img168.exs.cx/img168/7042/medkitthumb9rg.jpg
