I’m a nav for the Navy, so I can’t speak much for the AF. I believe the only tactical navs the AF has is in their F-15 2-seaters. There are plenty of HVAA (high value air asset, e.g., the EC-130, RC-135, etc) navs which are stand-off and rarely in a tactical environment. The Navy has tactical navs in the F-14 and EA-6B (3 of them), although they aren’t labeled as such. In the 14 it’s called a RIO (radar intercept officer) and in the prowler it’s called an ECMO (electronic countermeasures officer). The job is pretty varied from platform to platform, and even within a platform.
On a HVAA, you’ll probably progress from being a true nav (filing the flight plan, getting the many forecasts, programming the gps/inertials, plotting the course on a chart, taking ‘fixes’ along the way and telling the pilots where to steer to either get back on or stay on track, talking to ATC, keeping track of weather and gas (very important in the middle of the pacific)), to actually running recon or electronic warfare (jamming) missions, depending on the platform. No matter what you’re doing, you’re usually fairly busy, especially when things out of the ordinary start happening, like an intercept from a hostile country, in-flight emergency, in-flight rerouting, winds which are much higher than forecast, search-and-rescue.
The tactical-type navs in the prowler and tomcat are more focused on radar intercepts, bomb-run stuff, handling all the comms, and monitoring the electronic environment for targeting radars. Also, they have an extra pair of eyes to keep outside the cockpit to check for other air traffic and bad guy position for dogfights.
Almost all navs keep an official log of some sort or another when the plan is up in the air. This also helps to keep you busy.
FWIW, I’ve spoken to many AF navs, and they all say the same thing. The navs in the AF aren’t as well-respected as in the Navy. This isn’t to say the navs aren’t always below the pilots on the food chain in the Navy, but from what I understand, in the AF the navs get almost no respect at all for what they do. The saddest thing is that the AF navs don’t even get a bonus. The navs in the navy get a nice bonus. This may have changed very recently, though, so I’d check on it if you plan on staying in beyond your initial obligation. Also, flight pay is good thing.
Navs do not, fortunately, make coffee for people. 
Hope this helps.