Scavenger

From the Call of Duty Wiki

Scavenger is a Tier 1 perk appearing in Call of Duty: Modern Warfare 2 that partially restocks a player if they walk over blue bags dropped by enemy corpses, regardless of any loadout differences between the player and the dead player. The pro version allows the player to spawn with extra ammo, replacing the Bandolier perk from previous games. This perk also acts as a replacement for the X3 or X2 perks from the original game (such as Frag X3), since it allows the player to restock on equipment (hand grenades, C4s, etc.), special grenades, M203 grenades, and secondary weapon rockets and grenades, as well as regular ammunition.  "Spam" is not necessarily problematic with this perk: besides the fact that hand grenade throw ranges have decreased in Modern Warfare 2, players must do the following in order to benefit from Scavenger:

1. Expend any equipment they intend to pick up, since players cannot pick up more equipment than they have when they enter the match
2. Maneuver within close range of a fallen comrade or fallen enemy. 

Since running around blindly in Modern Warfare 2 does not generally lead to a long lifespan (thereby lowering the all-important kill-death ratio that motivates "spam" techniques), "shooting and scooting" in search of replacement equipment will be less than optimal.  Additionally: since a fallen comrade is likely to be within a kill zone staked out by opposing players,  and since a fallen enemy is likely to be followed by more enemies, Scavenger will most likely be useful to acquire extra equipment following a skirmish and less a source of unlimited equipment.

Technically, Scavenger does not allow the player to loot the body itself. Rather, it allows the player to see and pick up small blue backpacks that players drop upon death. These packs are what contains the grenades and ammo, rather than the body itself as the perk description suggests. They will not appear without Scavenger. If a player with Scavenger picks up a backpack, other players with Scavenger can still pick up that backpack.

Note that even with Scavenger, bodies will still drop weapons. With or without Scavenger, running over a same caliber weapon to your current weapon will NOT pickup ammo unless the weapon on the ground has the same camouflage as one already in your possession. For example, if you have a standard M16A4 and you run over an M16A4 with Arctic Camouflage your ammo count will not increase. Indeed, even picking up the Camo M16A4 will not increase the ammo for your standard M16A4. You will instead have two separate ammo counts, one for each gun, even though the bullets are exactly the same caliber. This seems to be designed this way to make Scavenger more useful. Without Scavenger, this often means you will be the only to be able to pickup ammo from your own dead body as only few persons else will be using an identical weapon camo. Well organized teams such as clans may consider standardizing their weapon camo to facilitate ammo transfer.

Scavenger is very useful for players who have weapons with low ammo counts to start with, such as the AT4, in which case it is possible to acquire more rockets from dead bodies. It will even replenish grenades, equipment and M203 ammo if applicable.  Scavenger is also useful for players who use Cold-Blooded (particularly with a Silencer) instead of Stopping Power.  In this situation, Scavenger helps compensate for the increased number of rounds it takes to take down enemy players.  Finally, Scavenger Pro is useful for snipers or players who spend a long time at distant locations, since their opportunities to reload will be few and far between: the increased starting ammo count will permit them to extend their stay at the location of their choice.

If a player using Scavenger has the Javelin unequipped, Scavenger will not replenish the Javelin's ammo. However, when the Javelin is equipped its maximum ammo can be exceeded by picking up a spare rocket. However, resupplying the Javelin does not resupply the player's primary weapon. This is most likely a glitch.

This perk is unlocked at rank 13.

The Pro version of this perk functions the same as the regular perk, except whenever the player spawns he/she will have full ammo. It functions the same as Bandolier from the previous games, except with the added non-Pro benefits.

[edit] Trivia

• Scavenger will allow you to pick up your set-up, for example a smoke grenade, from a dead person even if they did not have a smoke grenade when they died.
• Grenade Launcher replenishes with lost ammo and equipment. It will also replenish if it is selected. It will not replenish when ammo and equipment are both full.
• In the Xbox/PS3 version Grenade Launcher rounds will be replenished one round per backpack.
• Very rarely a glitch happens were you can have two frag grenades when resupplying.

Perks of Call of Duty: Modern Warfare 2
Tier 1 Perks	Marathon · Sleight of Hand · Scavenger · Bling · One Man Army
Tier 2 Perks	Stopping Power · Lightweight · Hardline · Cold-Blooded · Danger Close
Tier 3 Perks	Commando · Ninja · SitRep · Steady Aim · Scrambler · Last Stand
Kill Streak Perks	3: UAV Recon · 4: Care Package · 4: Counter-UAV · 5: Sentry Gun · 5: Predator Missile · 6: Precision Airstrike · 7: Harrier Strike · 7: Attack Helicopter · 8: Emergency Airdrop · 9: Pave Low · 9: Stealth Bomber · 11: AC-130 · 11: Chopper Gunner · 15: EMP · 25: Tactical Nuke
Death Streak Perks	Copycat · Painkiller · Martyrdom · Final Stand