So let's say you had a really awesome summer. You did a lot of fun stuff, relaxed, and enjoyed the sunny weather.
But wait! You let your practice routine slide!
Don't sweat it. Now is the time to renew your practice schedule so you'll be in fighting shape for back-to-school placement auditions.
Keep your routine simple to start, especially if you've been traveling a lot and haven't spent a lot of time working with your instrument. Give your muscles a chance to regain their strength and fluidity of motion.
I like to use scales and slow, melodic long tone exercises when I first come back to my flute after some time away. Any slow passage from your music will do; all that matters is that it has long note values and doesn't contain too many extreme register changes. I like to have a separate long-tone melody in my warmup for each register (low, middle, and high) so that I can really focus on the challenges of each of those registers.
Reviewing your major and minor scales will be invaluable to you, especially if your back-to-school band placements involve sight reading or scales. A high comfort level with those finger patterns will help you to do your best in auditions, even if you haven't spent the whole summer diligently practicing.
So don't worry too much if you haven't had the most productive summer, practice-wise. If you start reviewing now in a calm, organized manner, you'll be ready to sound your best for the new school year.