That pretty much obviates a lumbar pack such as The North Face's Dayhiker ($70; www.thenorthface.com), which is a perfectly fine pack but I think will just rattle around too much on your hips. I'd definitely think you'll want a hydration pack, something along the lines of the CamelBak Magic ($75; www.camelbak.com), a woman-specific hydration pack with a big bladder (72 ounces, or two quarts) and room for energy gels, maybe a light jacket, whatever else you might need. And it will ride fairly well.
You might also like Ultimate Direction's new Diablo pack ($80; www.ultimatedirection.com), which is equipped with a comfort-enhancing SportVest harness to keep the pack steady as you jog. An internal 64-ounce hydration sleeve will hold your water, while Ultimate Direction have answered your wish for pre-mixed fluids by including a 20-ounce bottle that rests in an easy-access stow pocket on the back of the pack. I'd estimate that this pack has everything you could possibly need (including two Gel Flask pockets on the shoulder straps).
Other options here might also include GoLite's 24 Pack ($80; www.golite.com), made specifically for adventure racers, so more than capable of handling gear and supplies for a long slog. Perhaps a little large for your needs, it has 1,200 cubes of storage space and a three-liter hydration sleeve.
As for what to drink, you have three choices. Choice one is to carry only water and supplement that with energy gels, energy bars, that sort of thing. They'll offer all the electrolyte replacement you need, largely obviating the need for Gatorade or a similar sports drink. Choice two is fill the bladder with your sports drink then rinse it thoroughly after the run so that the stuff doesn't start to mold. Choice three is to take some powdered sports drink, an empty sports bottle, and on occasion stop or slow down long enough to mix a little sports drink and use that to supplement your water.
So that's my advice on the gear. Good luck with this bit of insanity!
For more on hydration systems, check out Outside Online's Hydration Packs Buying Guide.
Support Outside Online
Our mission to inspire readers to get outside has never been more critical. In recent years, Outside Online has reported on groundbreaking research linking time in nature to improved mental and physical health, and we’ve kept you informed about the unprecedented threats to America’s public lands. Our rigorous coverage helps spark important debates about wellness and travel and adventure, and it provides readers an accessible gateway to new outdoor passions. Time outside is essential—and we can help you make the most of it. Making a financial contribution to Outside Online only takes a few minutes and will ensure we can continue supplying the trailblazing, informative journalism that readers like you depend on. We hope you’ll support us. Thank you.