Health Packs are First Aid Items found in Tomb Raider Legend and in Tomb Raider Underworld. They are similar to Medipacks, but there are only one size of them in both games. In Tomb Raider Legend the Health Packs rephelinsh Lara's health completely but the amount of Health Packs that can be in the Inventory is limited to three. Their appearance stays the same throughout the game. In Tomb Raider Underworld the Health Packs replenish about a half of the Health Bar. The appearance of Health Packs is different depending on the section that's being played. Sometimes the Health Packs that look like potions are referred as Natural Remedies. 
Description from PDA in Tomb Raider Legend
Standard field use medkit that will replenish health when used.
Description from PDA in Tomb Raider Underworld
This standard firts aid kit is equipped for use in mending cuts, scrapes, insect bites, gunshot wounds, and unidentified poisons.
Health Pack in Tomb Raider Legend
Health Pack in the Mediterranean Sea Section
Health Pack in Coastal Thailand Section
Health Pack in Croft Manor Section
Health Pack in Mexico Section
Health Pack in Jan Mayen Island Section
Health Pack in Arctic Sea Section
- Tomb raider Underworld booklet, PC version, page 16