Don't be shy about taking pictures! Some people avoid doing this because they feel it makes them look too 'touristy.' But all of your fellow passengers are tourists, and it's the staff is certainly used to tourists. So if the kids get involved in a dance contest, or the chandelier in the dining room is fabulous, feel free to snap a picture. If you catch them at the right times, the crew in uniform is usually very open and willing to get into a picture with you. Ask nicely when they're not busy, and get a great shot of the captain or a crewmember in full regalia. Get cheesy if you want to; ask a fellow passenger to take a photo of you and your spouse waving by the side of the boat. My parents took a cruise when they were first married, and their favorite snapshot from the trip is one of my father pretending to throw my mother overboard. Well, whatever floats your boat, as they say. Make it campy, make it silly, make it romantic... just make it memorable.
Keep in mind that if you're planning on making a scrapbook or a memory box of your trip later, the secret is to save, save, save! Maybe your ticket stub doesn't look like much while you're on the boat, but years later you will love to see it. Your room reservation holds valuable details that might just remind you someday that you had a western window or a terrible cot that folded out of the wall. Ask the waiter for copies of menus or carbons of your check so you can remember what you had at that memorable first dinner on the water. Save your slips from the casino if you decide to give your luck a try- it might make you cringe to remember you lost $50 in bingo, but at least you'll remember it!
So enjoy your cruise. Make good memories, and preserve them. Steal the soap if you must; but there are better souvenirs to be had. You just have to look for them!