According to the search results, the "Carry Forward" feature in Call of Duty: Modern Warfare 3 allows players to transfer certain content from Modern Warfare 2 to the new game. Here is a breakdown of what carries over:

What Carries Over:

• All Modern Warfare II weapons will be available for Modern Warfare III players, although each weapon’s associated unlock challenge must be completed before it becomes accessible in MWIII.
• Blueprints also carry forward, and certain Blueprints available via Store Bundles will also be available to purchase in MWIII.
• Weapon Charms, Weapon Stickers, Emblems, Loading Screens, Vehicle Skins, and Calling Cards will all be available within MWIII if you have unlocked them within MWII.
• Operator Skins.
• Completionist Camos.

What Does Not Carry Over:

• Tactical vehicles, particular lethal equipment, or Wartracks that are absent in Modern Warfare 3.
• Skins for vehicles and equipment that are not included in MW3.

It is important to note that some content may be unavailable if gameplay offerings are different in Modern Warfare III.