I remember hanging my backpack off the hook on the back of the baggage trolley, so that they didn't notice it...of course, that was back in the days when I didn't check in on the far right lane
But I remember one time that I had a wheelie case, and a backpack (and a coat!), and the wheelie must have weighed at least 25kg by itself - thankfully they didn't ask to weigh it when I checked in!