I recently bought a Thule bag. It’s hand luggage compatible and has a shoulder strap which can be removed and rucksack straps hooked on. I use 3 large packing cubes, trousers, tops, and smarter wear and a smaller cube for underwear. It wasn’t cheap, about £200 but it is amazing. I used it for 4 weeks backpacking in Vietnam and 4 weeks recently in Kenya. It has a laptop sleeve with it. I am lucky as I have a great part time job as the “Saturday girl “ in an upmarket hiking/travel wear and equipment shop in my small hometown. I am lucky enough to get a great discount on everything I need so I have a complete wardrobe of great practical clothes. I think that if I can’t get everything I need into this bag then I’ve got too much stuff.