I believe pre-paid tipping only covers your dinner serving team (Server, Assistant Server), your head server, and your stateroom host.
All other gratuities can be put on your KTTW card (for individual cocktails, etc) or cash (room service, port excursions, porters).
Only a couple cruises so far, but here is my understanding/experience.
As 'Ready' said, it covers server, assistant server, head server, and stateroom host.
Be aware that a 15% gratuity is automatically added for drinks. If you want to give the bartender or server more, you can add it to your receipt when you pay with your KTTW card (or give cash, but you have to sign the receipt, so we always just add to that when we want to add).
Almost everything from room service is free. So you probably won't have a receipt to sign. I brought a bunch of singles and tipped with those when the food was delivered.
As far as port excursions, plan on cash. Disney arranges the excursions, but they don't really run them. They are usually independent companies, so you're not going to use your KTTW card. If you want to tip, you should plan on handing someone cash at the end of the excursion.
There may be other places people tip that I don't know about. Especially if they involve the kids (kid's club, babysitting, whatever else) because we don't have kids and obviously, we don't do
everything there is to do on the ship.