Roving Networks RN-240 Bluetooth Serial adapter
You just can't buy a laptop today with a serial port, but most enterprise network devices need you to perform the initial IP address setup via a serial console. While there are a slew of Bluetooth serial devices out there, the RN-240 Firefly from Roving Networks has been the only one in my kit for nearly a decade and appears here again for 2014. I can literally plug this into a switch, router, etc., and work outside the telco closet or across the room. Since it even works with my Nexus 7, I have lots of choices for hacking that initial config. Kudos to the others of this ilk, but having a serial dongle that uses regular old AAA batteries is super-handy.