Kudos for including sound in the 2k.
* Use the mouse to move and click to shoot
* White bonus : Gain 1 life
* Green bonus : Upgrade weapon
* Title screen/main menu
* Game can be restarted
* Background stars
* Player ship and enemies ships
* Sounds using ZzFX
* Life bonuses
* Weapon upgrades
All of this under 2048 bytes zipped!