Someone else may be able to answer the excursion part, but as far as Johnny Rockets, there is a $3.95 cover charge (you may want to confirm the exact amount, but I believe it's $3.95) which is "all you can eat", except for drinks, but if you want to tip extra for your server you can; there will be a space once you get your receipt.
Just as with any excursion you would take here in the United States, you probably should tip your guides on the excursions, but like I said earlier, someone else may be able to answer this better than I can; I just though I would offer my input.
2007 - Majesty of the Seas (Bahamas)
2009 - Enchantment of the Seas (Western Caribbean)
2010 - Freedom of the Seas (Western Caribbean)
2013 - Golden Princess (Alaska, roundtrip from Seattle)
The best guidline I have seen for tipping on excursions suggests $5.00 for the guide and $2.00 for the driver on a half-day excursion (that's pp); double that for a full day excursion. Of course tipping is always discretionary. I've tipped a lot more for a really outstanding guide; and I've stiffed a few also.
One thing for certain: I always bump it up a little if they don't solicit a tip and drop it a little if they do.
Tipping is at one's own discretion. That said, this is what we do. We normally take sail/snorkel excursions. We usually tip $20. That we feel will cover every crew member. We will tip more if they really went out of their way. If it involves a bus ride to/from we tip the bus driver $5 at the end of the trip, if he at least tries to point out some things or gives us a little entertainment. We've had some that have sung songs, some that have given us history of the island, some that have given us some tour guide information. If we do a land tour, we normally tip the guide $10-$20 and the driver $5-10, depending on the length. This is not per person, this is total. We haven't eaten in Johnny Rockets, but I would tip extra if we did. Hope this helps a little.