One of the best tips I received before our first cruise was to take plenty of smaller bills! At the time I thought I understood the concept but once we were cruising I really saw how sensible this advice was for us.
TAKE PLENTY OF DOLLAR BILLS! We usually take about $50 in $1 bills. These are so handy for all of the little misc. tips and making change when shopping.
Most of our furniture sales are done in cash so when we get $1, $5, & $10, I stick them in a separate envelope to save for cruising! By the time we head out on a cruise we have a nice little stash set aside.
Some of the services you might want to tip are:
Drink/beverage servers (yes they do get paid but if you like faster service this helps)
Bathroom helpers on the islands (This is a big part of their wages and they work so hard to please the tourists and a $1 goes a long ways for them.)
Room service - you don't have to pay for the food (unless it's late at night or a specialty request) but I like to give the server a $1 or 2 when they bring coffee in the morning.
Porters when you drop off your luggage - they recommend a $1 or $2 per bag - but it's up to you
Tour guides and helpers
Your cabin steward - we always give them some money at the beginning of the cruise because I bring a small cooler for my diet Dr Pepper and $10 makes sure it's full of fresh ice every day! We also leave a little extra at the end of the cruise if we feel the service was good.
Dining wait staff at the end of the cruise for a job well done. If you use any time dining and like the service you can give the server a small tip each night.
This tipping guide is optional and not required.
I also take plenty of $5 and $10 bills for shopping on the islands. It's much better when you try to "bargain" for an item and can pay the exact amount rather than expect them to give you change back.
Don't take large bills or large amounts of cash on the islands. Just a common sense thing....
REMINDER: All of the purchases you make onboard are put on your sail and sign card so you cannot use cash for shopping, drinks, photo's, spa services, etc while on the ship. Heck you can even put your casino "purchases" on your sail and sign now!
Each cabin has a safe for your money and valuables.