The best size bag for traveling depends largely on your travel itinerary and mode of transport. The Cotopaxi Allpa packs range from 28 L to 42 L.
The 28L option makes for a compact and comfortable backpack that easily fits in overhead airplane compartments. The 42L option is a bit more like carrying a duffel bag on your back, but it still manages to fit in overhead compartments. It’s a great option for maximizing carry-on capacity in backpack form.