Although every trip has its specific considerations, the bags we recommend share a few similar criteria. They are all water-resistant to some degree, all of them pack down small enough to fit easily into a carry-on bag or to qualify as an under-seat personal item, and all hold at least 20 liters comfortably. We have packable bags that are great for outdoor adventures. We picked bags for city travelers and lightweight bags that stay dry in stormy weather. For space-conscious travelers, we have a pick that fits in the palm of your hand, and for those who would rather not carry a backpack at all, we have a compressible duffel bag.
Source: NY Times – Wirecutter