Yes, you can absolutely use a bag (such as a duffel, weekender, or large backpack) instead of a hard-sided suitcase for travel in 2026. In fact, many frequent flyers prefer soft-sided bags because they are more "malleable" and easier to squeeze into crowded overhead bins on smaller regional jets. For "Basic Economy" travelers, a backpack is often the only way to meet the strict "Personal Item" dimensions without paying extra. The primary downside of a bag is the lack of wheels; unless you use a "rolling duffel," you will be carrying the full weight on your shoulder, which can be taxing in large hubs like Atlanta or Dubai. However, for 2026 adventure travel or "hop-on-hop-off" train trips in Europe, a high-quality travel backpack (like an Osprey or Tortuga) is often superior to a suitcase because it leaves your hands free. Just ensure the bag has lockable zippers and enough structural integrity to protect any fragile items, as soft bags offer less impact protection than hardshell luggage.