But that everyone knows the music is exactly what makes this repertoire so much fun! You can insert "jazz improvisations" (in my studio we don't make mistakes in performance, only jazz improvisations) into the music (planned or unplanned). But even better, this is a great opportunity for you to start to make the easy leap to generating your own arrangements.
If you are skittish about doing your own arrangements, you might start by staying very close to an existing arrangement (many people would consider this still their arrangement - but the important thing here is to start to flex your arranging muscles in a safe way). You could use lead sheets to let yourself go. Or, as I noticed I was really doing this year, you can just work on those little jazz improvisations building them into your own arrangements.
Because, let's face it, much of the music of the season has a tendency to be trite. If everyone plays all the same tunes in the same way in the same arrangements, how will you every stand out (and not go barking mad)? Easy - amp up your own arrangements!
And don't forget to note how you amp those arrangements up - you could use them again next year!