There are several incarnations of Rat Pack.
The Rat Pack are an elite paramilitary cadre of scavengers, thieves and looters-for-hire. This gang of criminals use numbering system as code names. Their main purpose is to raid and salvage everything they can find. They are arguably the best in the world at what they do, though thankfully there's not much competition. They are professionals.
They are not fools. Even the battle could be lost they know their first priority is fullfilling their contract.
Once Super-Skrull masqueraded as their leader.
The original Rat Pack were created by Roy Thomas and Gil Kane. They first appeared in Captain Marvel #20 - The Hunter And The Holocaust! in 1970.
This Rat Pack is an elite group of enforcers that work at the Synge family's casino. They opposed the X-Men 2099 during the memorial service for Noah Synge.
The RatPack is a motorcycle gang that works for John Howlett in Las Vegas.