At the most basic level a tuning kit needs:
File(s) one 12" and one 8" (large one for base filing, smaller one for sides)
File card to clean files
P-tex candles to fill gouges
Iron (even an old house iron will get the job done if you set it carefully.. hot enough to melt but cool enough so the wax isn't smoking).
Ski Wax Kit (usually three different colors for super cold, average and warm days)
Plastic Scraper to scrape wax
Metal Scraper to scrape P-tex repairs
Cork to smooth wax that is rubbed in instead of ironed on.
Lighter to light P-tex
Stone to remove burrs and quick tunes
Stuff you will probably want:
File guide for more precise bevels
Large phillips screwdriver (or gun bits) to fit binding screws
Ski specific vises for workbench
Scotch brite pads-similar to cork, but removes dry base bristles too
Soldering Iron for P-tex instead of open flame method
this could go on forever, just look at the tuning bench threads LOL!