I have travelled with Vuelling 3 times since my post. Each time with a normal sized backpack (but probably too big to stow it under the seat in front of me) without any issues.

I doubt you will be able to take a roller bag/trolley onboard without having paid the 10 Euro for a cabin bag, but again no first hand experience. At BCN I saw a pax being asked to pay at the gate for trying to bring onboard a trolley.