A holdall differs from a suitcase by its flexibility: it can be compressed, stored flat, and accommodates irregular shapes. Now, you just need to choose how to carry it, whether on your shoulder, on your back, or with wheels.
The travel bag sits between hand luggage and a suitcase. It lies flat when empty, accepts irregularly shaped items that a suitcase cannot accommodate, and can be carried in various ways depending on the model. Its downside is the opposite of its strength: it offers less protection.
There are three carrying options available, and they are suitable for different journeys.
The Duffle bag is a cylinder with a long opening, derived from the seaman's bag. It swallows up volume and squashes down, but you have to rummage around to find your things. A classic travel bag, more structured, opens flat like a suitcase and maintains its compartments. The first is suitable for sports and weekends, while the second is ideal for organised travel.
A travel bag is chosen in litres, like a backpack. Below 40 litres, it often fits in the cabin and can replace a suitcase for two nights. Between 50 and 70 litres, it covers a week. Beyond that, the weight when full becomes the real limiting factor, well before the available volume.