Which size of SealLine pack or duffel should I pick?

Our dry packs, dry daypacks, and duffels are sized volumetrically in liters. To help illustrate how those volumes translate to real world use, here are some general ideas of what fits in various sizes of our packs and duffels:
 

• 20L = a common day size; fits most items one would carry on a day trip
• 30-40L = a small weekend size; fits most things you’d carry for an overnight trip
• 70L = a long weekend size; fits a couple days’ worth of gear and food
• 115L+ = this is the largest size we make; think of this as the “everything and the kitchen sink” size—it holds a lot of stuff