GPS , On-Screen Display and Data Logging
GPS with a On-Screen Display (OSD) can be a handy tool for FPV piloting. The GPS unit is connected to a OSD and overlays the info on the FPV pilots monitor or Goggles, usually in the corners of the screen.
Most companies that produce OSDs for RC come with or have an available GPS module and data loggers that connect easily to their OSD board which is what I would recommend to keep the hook-up simpler. Data Loggers like Eagle Tree Systems eLogger v3 are necessary componet nowdays. Data loggers have hook ups for hardware and sensors like OSD, GPS, RPM, Temp, Speed, Altitude, Battery volts, etc...and then can be overlaid on the viewing monitor.
There's also some newer OSD's coming out that will have artificial horizons sensors that will help the FPV pilot with more info on climb, descent rates, level flight and amount of banking in a turn. This part of the display will be helpful when flying through fog, dust, low clouds and my favorite...Night Flights.
In order for you to see the GPS and sensor info on your screen all you need to do is connect the FPV camera to the "video in" and connect the wireless transmitter to the "video out", along with connecting the GPS /sensors If needed). This will allow the info to be overlaid on your screen. Then supply the recommended power and that's it. This is the basic OSD but they can be much more complicated if using RTH due to programing but even still it's not that difficult.
OSD's are nice to have but not totally necessary for FPV flight. They might take you a little more time to set-up at the flying location, you may have to wait for the GPS to locate enough satellites before there's any info available which is only a minute or two. They also add more wiring to your aircraft so keep this in mind if you go with an OSD,GPS and a Data Logger.
When purchasing a OSD we recommend going with one that has Firmware update abilities through a USB/Internet connection. This makes things a lot easier when there's a software up-date available.
Eagle Tree Systems, New Generation Hobbies, Future Hobbies, and Hobby Wireless now offer a faster 10hz GPS/OSD. Some of these newer OSDs have RTH (Return To Home) feature when using them with a GPS like Eagle Tree's OSD Pro. So if radio signal is lost or glitching the OSD RTH will take over the plane and fly it back to the pilot until radio signal is regained.
NOTE: RTH does not work with RC helicopters at this time. 
In the Driver seat with a FPV Traxxas E-Maxx
Adding a Dashboard for FPV Piloting
Dashboards are a cheaper way of gaining basic on-board information like battery voltage, altitude, air speed, heading, etc... viewable through the FPV pilots camera rather then using a more expensive OSD. Dashboards can be anything you want it to be and are usually some type of monitoring/metering of the aircraft/vehicle viewed through the pilot cam. They are mainly mounted in front of the camera where a pilot can see the info at a glance or mounted a little below the cameras view where a pilot can tilt the camera down to see the information.
Most often FPV pilots use a common LED bar type display to monitor the voltage of a battery which is very useful on long flights. There are all kinds of different monitoring an FPV pilot can do with a dashboard in view. I've seen things like a small bubble compass mounted on the aircrafts nose that worked for heading and as a bank indicator. A piece of thin plastic strip with a red tip taped on the nose as a speed indicator and the list goes on...and what attracts me to a dashboard is the simple and cost affective way to gain the aircrafts basic info without having a OSD or using much battery power or if any at all.
When looking at adding a Dashboard keep in mind that you must be able to see it in bright sunlight and some displays may not be readable with the suns glare. Some pilots have mounted visors to their dashboards protecting from the sun glare. Others have found ways to sink the dashboard into the fuselage or nose adding even more protection. Also the dashboard or monitoring/metering devices don't have to be mounted on the nose, as you could place it anywhere that you can pan/tilt your pilot camera for observing the info when needed. Other things to consider is the focus of close by objects and most FPV pilots have their focus set at a further distance rather then up-close or macro so keep your dashboard mounted far enough from the camera to be viewable. This is another reason I go with large basic displays.
GPS used as dashboard in Twin Boom RC plane
Lipo battery alert placed by a mic can help when battery is low.