Rocket League's Frosty Fest will start December 11 and run through January 2. This event will work similarly to the Halloween event in that it will have its own currency -- and this time, it will be Snowflakes.
Snowflakes will be earned by playing matches and can be used to buy event items, decryptors, and the new Frosty Fest event crate (as of this writing, no details were offered on specific rewards).
Note: the stand-alone items you can buy are not the same items that will be available in the crate. The Frosty Fest event crate will be available as an occasional drop after matches, purchasable using snowflakes, or available using real-world money.