RCCL...aka "The RCL", doesn't have too many extra charges, but a few do exist. The ones that come to mind are the charge for sodas that are included on DCL, the $5 (I think) per child per hour "Babysitting fees" that are charged after 10pm and upcharge restaurants that some parents may feel pressured into taking the kids to like Johnny Rockets.
The $20 towel rental fee is a new one on me and I think it's ridiculous, but that charge is easily avoided so doesn't really count against RCCL any more than the $250 charge for losing a Wave phone would on DCL.
I agee about the towels...to a point. The wave phones will have individual ID's. So if someone loses their phone, they cannot just grab yours and claim it as their own to avoid paying (sticking you with the fee). Plus, in general, you are going to leave your towel on a chair at the pool much more casually and more often than you would set down a phone and walk away.
Jess