Relax American tipper.
Sorry , I just think it's funny how you guys worry about stuff.
Anyways, you didn't say which line you were going on, and so I can only advise on Princess from my own experience.
Tips for all bar purchases are added to your bar bill automatically(15%) . You just sign the slip.
One dollar bills ( American of course) are mainly used to tip the room service personal, tips range from $1 for coffee/tea to $5 bucks for a meal. Keep a stack of them in your safe to hand out, you won't really need them anywhere else on the ship as everything else is a " cashless " society( just have your sign and sail cardwith you)
In Europe I would think that if tipping the land based tour operators that Euros would be nice, but I am sure they like dollars too( or they used to when I was there 3 years ago, but now may be it has changed)
As for amounts, well that depends on you, I didn't use room service much as our cabin was on the same deck as the buffet so it was just as easy and quick for us to go grab a plate and bring it to our room ourselves.I can't see anyone needing more than $5-7 dollars a day for room service( unless you eat every meal in your room( which is weird)
Tour guides, well that depends , are you on ships tours or privately arranged ones? I would tip more for the privately arranged ones, the ships shore exes are always so much more exspensive that I figure they have built in a decent wage for the guide. I still tip, but not as much.I wouldn't tip more than $5 for a shore ex, and that's only if they actually crack a smile. For a private tour , I would reconsider that amount.