(Credit: Sky One)
Cubits are a form of government-regulated currency used throughout the Twelve Colonies prior to the Cylon Attack (Mini-Series).
The cubit typically comes in two forms: coin and paper (Mini-Series).
The paper version comes in denominations of 1, 5, 10, 20, 50, 100 (logically assumed) and even 1000 (Colonial Day).
Currency became worthless in the eyes of some, particularly Tom Zarek, because it was a vestige of the "old ways" that the survivors clung to. Despite this, Wallace Gray was instrumental in creating and maintaining commerce in the fleet, so this form of currency is still utilized (Colonial Day).
It is assumed that cubits became the common currency after the Articles of Colonization were passed.