"Bullet(s)" is an obsolete term that has accidentally survived on the Space Station card "Armoury". It refers to a game mechanic similar to Neon Rush, which has replaced Bullets.
The obsolete term "Bullets" should not be confused with a few Items that have words of similar meaning in their names, like "Rubber Stun Rounds" and "Riot Control Rounds". Those Items are fully functional in the game. But the "Armoury" Space Station room card is obsolete, and its function has been taken over by the "Soda Bar" room card.
Neon Rush
Neon Rush is some kind of performance enhancing energy beverage in the Chronicle X universe. Each Hero starts the game with a six-pack of them, and they can be spent to reroll the Hero's own Combat dice, one Neon Rush token per die they want to reroll.