When the Last Ship Sailed
The most straightforward way for a player to use XP is to reroll any roll in the game – even one that she didn’t make. This costs 1 XP per reroll, and the player chooses the best result. She can continue to spend XP on rerolls, but this can quickly become an expensive proposition. It’s a fine way to try to prevent disaster, but it’s not a good idea to use of a lot of XP to reroll a single action over and over.
A player can also spend 1 XP to refuse a GM intrusion.