My 3.5 yo DS has a Crayola brand wheeled suitcase with backpack straps that I bought at at thrift store for $3. I originally intended it just for playing "vacation" around the house, but on our August trip DEN-MCI he insisted on bringing it stuffed with his IFE, lovey, and snacks. I'd say he wheeled it 90% of the time - we did take charge of it on escalators and getting on the train at DIA and the car rental shuttle at KCI, but otherwise he was very proud of "his" suitcase.

I'm not sure we'll use the backpack straps - the bag itself is bigger than his torso so I don't think he can wear it easily.

I read reviews of the trunki on Amazon but was not impressed enough to part with that much money.