What item drops can I get?

Solution 1:

For item drops, it boils down to 5 categories:

1. Weapons
   • Individual skins that drop are parts of certain Collections
     • A year ago-ish several of the original weapon collection skins were retired, meaning you cannot receive them as a drop from the item-drop system
     • Collections that you can currently receive item-drops from
       • The Train Collection
       • The Mirage Collection
       • The Safehouse Collection
       • The Italy Collection
       • The Lake Collection
       • The Dust II Collection
       • The Bank Collection
   • Weapons originating from Cases cannot be found as a drop
   • StatTrak weapons cannot be found as a drop
2. Cases & Capsules
   • There are always 3-5 cases in rotation in the item drop system
   • As new cases come in, old cases are phased out.
   • Some cases are for Operation pass-holders
     • For instance, the current operation is called Operation Breakout, with a case called Operation Breakout Case
     • This means that the Operation Breakout Case will drop for only for Operation Breakout pass holders
   • Older Operation drops are available to anyone, but this usually up to Valve's discretion
     • The previous Operation, Operation Phoenix, had it's own case specific for its own passholders, called the Operation Phoenix Case
     • The Operation Phoenix case used to be only for passholders, but can now be received as an item drop by anyone
   • Sticker Capsules can drop
   • Exclusive Sticker Capsules cannot drop. For example, the Katowice 2014 Challengers capsule (had to be bought in-game)
3. Missions
   • This was introduced in Operation Breakout
   • Missions WILL not drop for players without the Operation Breakout Pass
   • Completing a mission will give you a weapon drop from 3 specific collections:
     • The Baggage Collection
     • The Overpass Collection
     • The Cobblestone Collection
     • This means the above 3 colletion weapons CANNOT be found through regular item-drop system

4. Souvenir Packages

   • There are sometimes tournaments that come around that Valve designs Souvenir packages for. By linking your CS:GO account to a Twitch account or GOTV account, you can watch matches and have a chance to receive a Souvenir Package after a match ends
   • It doesn't matter if you've paid for a ton of skins for the game or never spent a cent on the game, you can get Souvenir packages regardless.

5. Graffiti

   • Valve released a new update to CS:GO. It include graffiti/spray as well as other fixes. Most of them are Paid Sprays.
     • However, you can still get a basic spray as an item drop.

Solution 2:

Knives, StatTrak weapons, and keys can not be dropped in-game or from a mission. Knives and StatTrak weapons can only be obtained from opening crates or bought on the Steam Market while keys can only be bought from Valve or the marketplace.

Sources:

• http://steamcommunity.com/sharedfiles/filedetails/?id=170746735
• http://blog.counter-strike.net/armsdeal/faq.php