Grenade Bags

In the Call of Duty series, Grenade Boxes (or Bags) carry grenades for the player to pick up. In Call of Duty 1 and United Offensive, they were at preset locations and couldn't be picked up from troops. From Call of Duty 2 on, grenade boxes could be dropped by enemies.

Call of Duty 1 and UO
In Call of Duty 1 and United Offensive, grenade boxes were at preset locations and could not be dropped by enemies. In those games, grenade boxes contain 10 Stielhandgranates, which is the maximum amount of grenades you can carry. The picked up grenades appear when you run out of the grenades that you're supplied with at the start of the level. In some cases, a grenade box is the first time you'll encounter grenades in a level.

Call of Duty 2
In Call of Duty 2, grenade boxes (now bags) are dropped by random enemies. They contain three Stielhandgranates, but no smoke grenades. Mk2, RGD-33, and Mills Bombs don't come in bags, but still contain three grenades.

Call of Duty 4
In Call of Duty 4, troops randomly drop grenade bags. Each bag has one frag grenade and occasionally a Flash grenade.