My bet is battery also. You say that you spent a lot of time idling in traffic maybe with your airconditioner or heater going (depending on climate wherever you are), your tunes playing and maybe lights on. A marginal battery probably got stressed to death. Original battery? If so it died a natural death.
A/C is not much consuming electrical power other than the heater blower and if the alternator is good, the car would still charge the battery when idling. The OP should have mentioned the jump start attempt, this makes a difference on the likely fault.