Shoulder seasons (spring and fall) generally allow shorter notice, though holiday weekends like Memorial Day, July Fourth, and Labor Day sell out early everywhere
Lastly, also regarding air travel, the lack of structural support actually allows you to overstuff a 40 liter bag to the extent that it no longer fits airline carry-on dimensions
Some are good and some are pretty useless, indeed it amazes me how such an awesome brand as Simms can make perhaps the worst yet most expensive studs I have ever used for example
It also comes with a dust bag, to help keep it clean when it's sitting in the closet in between trips

Traveler Luggage Ultralight Backpacks UNDER ARMOUR Underseat Luggage Unicorn Backpacks Vans Backpacks Vans Checkerboard Backpacks Vans Disney Backpacks Vans Old Skool Backpacks Vans Realm Backpacks Vaschy Backpacks Vegan Backpacks Vera Bradley Backpacks Verdi Luggage Victoria's Secret Backpacks Victorinox Luggage Vintage Backpacks Volcom Backpacks Waterproof Backpacks Wenger Backpacks Western Backpacks Wheeled Duffel Bags Wheeled Garment Bags White Backpacks Women's Luggage Womens Backpacks Work Backpacks Wrangler Luggage YETI Backpack Coolers Osprey Packs Daylite Daypack, Eggplant Purple Brand: Osprey Color: Eggplant Purple Features: Large panel loading main compartment provides accessibility to inside contents Dual stretch mesh side pockets provides additional storage options The multi-function interior sleeve can be used for either a reservoir, tablet or laptop (up to most 14" laptops)
My loadout may be a bit overkill, so yours could possibly fit just in the front two compartments