I've not used laundry services on the ship, so I can't comment.
I have always just taken cash. The exchange rate is set by the government and there is a bank right in the Marriott so you can convert cash as soon as you arrive. A banker will come on board the ship to exchange cash later in the trip as well if you need more.
Try to make certain your cash is in good condition. Old worn bills, bills with tears, or with writng or stains on them may not be accepted for exchange.
You can use American dollars, they are accepted most everywhere, but you'll save a little using Egyptian pounds to buy things. For larger expenditures, most stores and restaurants also accept credit cards.
Extra 1$ bills are good to have with you for the people who clean the rooms daily, and to purchase small items. You'll hear vendors shouting "one dolla" often. Tipping (baksheesh) is an expectation for any small service. Bathroom attendants, taking someones picture, etc., two pounds or so is usually sufficient.
Speaking of bathrooms, it's a good idea to bring tissues to can carry with you. Some toilet facilites may not have sufficient (or any) toilet paper or towels. As with most any foreign country, drink only bottled water.
My best advice is to enjoy Egypt and its people. Most everyone you meet will speak some English. The people are always very friendly and gracious. Enjoy your trip...