For year round outdoor adventuring, a midsize (33-40L) expandable backpack is the best thing ever. A larger capacity allows you to use the pack for family trips (Mo-o-o-o-o-m, can you hold this?) or winter pursuits (hello, puffy jacket!) and ensures you can pack all the safety essentials you need and creature comforts you crave.
Bigger does not have to mean heavier! With the materials available today, it's possible to get a large and light backpack with thoughtful features such as rain cover, hiking pole loops, compartments and more. Weighing in at little more than my 28L pack, my 33-40L pack allows me to stow everything IN it rather than hang things off every strap.