Rats are known to have fantastic memories when it comes to having ingested a poison that made them sick, but does not kill them -- they will forever avoid anything that contains even a trace amount of that poison. Additionally, as has been previously pointed out that Warfarin (and other poisons) are just not as effective at killing rats because of the development of some immunities ... so I would go with Resist Poison as one of the racials. (I wish there was a DETECT POISON racial).
For the other racial, I would think that DODGE would be a good one ... ever try to hit a rat with a stick, shoe, or rock? They are pretty good at dodging their attackers.
While rats have claws, their teeth are much more dangerous weapons. So, I could see CLAWS as a possible racial skill, if you would like to fight with claws.
My choice, if I where to play a Rat scavenger, would be RESIST POISON and DODGE.