We use Room Service more than most people (usually twice a day), so for a 7 day cruise I'd take at least $30.00 in ones. I generally leave them in an envelope next to the safe where they're easy to get to. (No, they've never "disappeared".)
When you give your luggage to the porter before you board, I'd recommend a $2.00 per bag tip. (If we have two big bags we tip $5.00, it's just easier.)
The on board auto-tip and the 15% drink tip will cover everyone else on the ship, but you can tip extra to staff who go "over and above" the expected service.
If you take an excursion and find it fun and interesting you might want to tip $5.00-$10.00 to the tour guide and driver.
Almost all of this (except the auto-tips) are really up to you.