luggage question

Hi everyone, just a question regarding the type of luggage you can bring, still not sure after reading contikipedia..

the bag im bringing is like a backpack with wheels and has a detachable day pack on it. if i keep the daypack attached and the total weight is still within limit can i count that as my one suitcase and then have a handbag on the bus?

Also, bit confused with the metal framed backpacks..i have a 'caribee fast track' and i dont know if this is considered one? there is bar at the back of it which may be metal..it keeps the backpack straps all in line etc.

thanks