I use HeroLab by Lone Wolf Development to track my characters. I know other people have just used regular spreadsheets and such.
Now that the rules in the Roleplaying Guild Guide have changed to make it allowable, I'm in the process of moving over to using scanned chronicles and spreadsheets for the ITS. This is very much a work in progress.
I use a PDF reader (Goodreader in my case) for viewing the PDFs of the rulebooks. Since HeroLab will tell me which book something comes out of, that works relatively well.
To my knowledge, neither Goodreader nor HeroLab are available for Kindle Fire.
LWD is producing an option called HeroLab Online that is supposed to allow you to use any device to access your characters. I have not used that product so I can not comment on how useful it is.
There should be other options for the Kindle Fire. I know that you can send PDFs for conversion to Kindle format so you shouldn't have any problems viewing your rulebooks.
I use Masterwork Tools: Pathfinder Open Reference for the rule books on my Kindle Fire.
Seconded. Pretty much my whole gaming group uses Masterwork Tools. I also use Pathbuilder and Spell Tracker.
I love having my rulebooks available on my tablet, particularly when I go to conventions. Not having to lug around a satchel of books is, by comparison, delightful.
I use a spreadsheet for my charactersheet, and write most of my spells/extracts in there. If i dont, or I acquire a new ome in session, I'll use the PRD/d20PFSRD to look up the spell.
Apple Tablet, Polaris Office. The spreadsheet program was a lot cheaper than getting Hero Labs and from what I have read, more reliable.
I keep my spreadsheet at home up to date and update the charactersheet on the tablet regularly. I can even email the character sheet to the GM when they want the update after I level.
I used a Samsung NotePro 12.2" (Android) for a couple years, and it was... adequate. Full PDF library of my rulebooks... fine. Masterwork Tools as mentioned above... good. Tablet browser... okay.
When it died, I went back to a laptop, and won't look back. Having an actual keyboard is useful. Having a full multi-browser choice is useful. Having a fully-featured PDF viewer is useful. Sure, it's (much) more expensive than a tablet, but you get what you pay for.
the Pathbuilder App is great for quickly putting a character together and can generate a character sheet or stat block pdf. I have it on my android phone.
Other than some painting apps for sketching out battlemaps/dungeons, the internet for d20pfsrd, the Pathfinder PRD, and PathfinderWiki, the Google suite is pretty much all I need.
I own a PC and an iPad Air 2. I use Herolab for character creation. I use an app called Game Master (GM) for campaign creation and running the game (same developer that makes Fight Club). I also use Goodreader for storing, accessing, and searching my digital books (PDF).
I encourage my players to keep a digital character sheet (Myth-Weavers) so I don't have to borrow their physical copies to update my information in the Game Master app. I also use Herolab to store my players character data and ensure everything is legit.