I bought a kit last fall so I can tell you what I personaly found useful as a begining tuner. (still am a beginner)
Most of which is echoed above.
At least a diamond stone to follow the file
Gummy for removing rust spots and other things
Binding ties - I ditched the expensive ski specific ones. I got a big bag of giant rubber bands from an office supply store for like $1.50. Work like a charm and if it pops off and flies across the room, I don't have to go look for it. LOL
Lots of extra wax to practice with. I spent a lot of time with an old pair of skis with broken bindings just practicing. I don't touch my good sticks without trying it several times on the broken ones first.
I picked up a full set of brushes stiff nylon, horsehair, brass, and soft nylon.
I opted not to get a scraper sharpener. I use a jig and sandpaper. Seems to work just fine for me.
Oh, and again. Read every thread and watch every video. Helped me a lot.
I'd also give a shameless plug to Dr. D at Racewax.com He spent a lot of time with me on email helping me get just what I need, not too much overkill, changing packages to fit my needs, and even wrote on the packages how and in what order to use what. Total top notch!
My Ski buddy laughed at me starting to do this myself. Untill I skied with him last year. He no longer laughed.
This year, I'm looking at picking up some more different stones and maybe a true bar.