It's canon that the Pip-Boy (extending back to even the 2000) had map, motion sensor, geiger counter, and notetaking capabilities. Keep in mind that this is a device designed from the ground up to be the end-all be-all for utility purposes.

From what VATS has been shown as throughout the games, it's not a "stop time and Deadeye shoot the baddies", it's more of a targeting assistant that somehow takes an assessment of the situation (windspeed, shakiness of the user's arm, size of the target, properties of the weapon used) and gives a rough estimate of how likely you are to hit whatever target you're aiming at. 

Just going by what's absolutely canon and not what's demonstrated through gameplay, I'd say the PipBoy would have:
[list]
[*]A radiation monitor
[*]An atomic clock
[*]An electronic notepad (would act as a rudimentary questlog and inventory, though it wouldn't automatically update and it doesn't store objects in hyperspace)
[*]A map (that you presumably have to draw in as you go)
[*]A radio receiver
[*]A biometric lock
[*]A basic targeting system that basically just gives you a rough estimate of how likely you are to land a shot on a specific part of the enemy (VATS).
[*]A built-in flashlight function
[*][i]Possibly[/i] a mass spectrometer, for determining the nutrition and toxin content of food and water
[*][i]Possibly[/i] a health monitor, for diagnosing injuries and diseases.
[/list]

Of course, this model of the PipBoy could have all of that, some of that, or [i]none[/i] of that, it's all up to [@Vertical].