I personally have an iphone and I use the living heck out it when going out for a shoot - planned or otherwise. Here's my list:
Top of my list. I use it to bookmark locations that may or may not be interesting in the future. I'll pull over and roll down the window, then whip out the phone and drop a pin fairly frequently.
- Camera or hipstamatic
I really love the camera on the phone, and these days I never record anything without snapping a pic of it. Hipstamatic is cool. Here's a tree I recorded today shot with hipstamatic. It makes me happy. :)
DB meter and bit calculator so that I can see how much space I have on my cards at various sample/bit rates. The dictionary is kind of interesting too.
probably the best weather app available - has moving doppler radar, forecasts and even webcam views.
pdf readers that can download files locally so you don't need interent access to grab them. I use them to store manuals and other useful technical stuff on the go.
productivity and listmaking app. Great for putting together checklists for project and equipment. I use it both in macro and micro contexts - making sure that my various projects don't take on too much rust while helping micromanage the stuff i'm working on right now. Syncs with todledoo and remember the milk.
regular notes, voice notes, picture notes with geotagging, freehand drawing, and a web broswer. I mostly use it to snap a photo of something and add a note to the photo - often for when I find an interesiting location to record. The photos it takes geotag and integrate directly with maps, and each photo has spots for notes. really great for grabbing something that you'd othwerwise drive by and forget about.
not an app but a website that I access from my phone when on the go. live air traffic tracker, and iphone compatible.
ok, what did I miss? what do you use on the go, and how do you use it? mobile websites anyone? android?