Here are a few resources that may be useful for flute players...

Scales

Why do published scale exercises generally cover only two octaves? Here's some scales that cover the full basic range of the flute (C4 to B6), in major, minor harmonic and minor melodic varieties. As a band conductor once told us, just practice these 3 hours a day for a couple of years and you'll have them down pat!

Scale exercises: scales.pdf

Double Tonguing

Trevor Wye has some nice double tonguing exercises in his Practice Book for the Flute, Volume 3, Articulation. They're all variations on an exercise by M. A. Reichart. Unfortunately, he doesn't have space to write out the full variation in many cases, and just provides a couple dozen of bars to establish the pattern.

However, I find it's hard enough just trying to get my stupid tongue and fingers working in sync without having to work out what it is that I'm supposed to be playing at the same time. So here's all the exercises written out in full. As before, a couple of years of playing these every day should get you up to speed.

Double tonguing exercises: doubletongue.pdf

Trills

Paula Robison has some trill exercises in her Flute Warmup Book. But in this case, they're limited to one actave only. What is it with these exercise writers anyway? Anyway, here's trill exercises covering the full basic range of the flute in all of the major keys.

Trill exercises: trills.pdf

Key Signatures

There's a simple technique for determining the number of sharps or flats in any major or minor key, and determining which of the notes are to be sharpened or flattened. I have't seen it described anywhere else, so I'll add it in here.

All you have to remember is FCGDAEB, which is the first seven notes in the circle of fifths starting with F. One way to remember this is via a mnemonic. The standard is "Father Charles Goes Down And Ends Battle". I prefer the more up-to-date "Foolish Canadians Get Drunk After Entering Bar", but maybe that's not suitable for younger musicians.

All you need to do is to write out that sequence three times, once with flats, once as naturals, and once with sharps:

F C G D A E B F C G D A E B F C G D A E B

Now, for major keys, we just count from C natural, with sharps on the right, and flats on the left. For minor keys, we do the same, but starting from A natural.

major keys:     6 5 4 3 2 1 0 1 2 3 4 5 6            
  F C G D A E B F C G D A E B F C G D A E B
minor keys:           6 5 4 3 2 1 0 1 2 3 4 5 6      

Furthermore, the table tells you which notes are flattened or sharpened! For sharps, just read them off from the middle row in left to right order: F, C, G, D, etc. And for flats, read them from right to left: B, E, A, D, etc.