Hi,
There's loads of stuff you could do. Do you have any grade seven pieces already prepared? When I first started uni I used my grade eight pieces to audition for stuff as it saved me learning new ones, and I already knew my grade eight ones must be good enough since I got good marks in the grade eight exam and for A level where I played the same pieces for my recital.
If not, there are a few things I could recommend. If your audition is long enough to play more than one piece, go for a range of styles, and choose mainly pieces which have a piano accompaniment so that you can show how you fit in with another player. For classical, I'd pick up a copy of the Handel Sonatas book and pick something from there. The first and second movements of the E minor were on grade 7 when I did mine, and the first and second movements of the C major were on grade 6. The A minor is also very nice. You can't go too far wrong with the Prelude from John Rutter's Suite Antique either, which was grade 6. And if you want to show off, go for Russell Stokes Jazz Singles no 4 (I know there's no piano accompaniment, but it's a great piece - it used to be on grade 7 but sounds harder). Although people will tell you the Mozart concertos and the Poulenc Sonata are staple diet for flautists, none of them come up before grade eight so don't be tempted if that's not what you want.
Best of luck,
Helena