Being a first-timer myself, I have relied on those more experienced to give me hints about all of the essential items. I started a spreadsheet for each one of us for packing (which sounds anal retentive) to keep track of everything! Someone mentioned a miniature sewing kit, someone else suggested a shower cap and a wise cruiser mentioned baggies (both for clothes and for various liquid items which might spill during transit) and a bungee cord. The baggies could also be used for bringing back things (I have a friend who wants me to bring back sand for her collection) and for tucking your valuables into (but not your wristwatch, please) to take with you while snorkeling. The small first aid kit containing over the counter items such as bandaids, antibiotic ointment, sunburn cream, upset tummy medication, allergy pills and linament is already in the suitcase permanently, just in case.
The packing list I mentioned came in handly a few weeks ago when we had to head out of town in a rush for a family funeral. I just omitted the swimsuits and shorts and substituted appropriate funeral clothing, and away we went. When we got to the airport, I was glad that I have already purchased plastic envelopes, clips and neck chains to hold our cruise cards while on board (we have to wear ID badges at work, so this is nothing new for us) and leather boarding pass holders which everyone is getting for Christmas, as you have to provide ID at the ticket counter and again when you board the aircraft. It's a pain to have to keep hauling out your drivers license or passport all the time. You should look into that kind of thing if you plan to travel frequently.