Laurie,
I belong to the OA (Overpackers Anonymous) so I may not be the best response you will get but here is my list.
First Aid Kit - Aspirin (painreliever for adults & children), bandaids, anti-septic for scraped knees, something for upset stomachs caused by excitement etc), something for motion sickness as it is too late after someone gets sick to stop it, they just have to ride it out for the most part and any other meds that someone is taking.
Sunscreen
Hairdryer - the one in the bathroom is worthless IMHO
Extension cord
Cameras and extra batteries and chargers
Highlighter - or something to mark your Navigator so you remember to do the things you read
Cruise documents - even if you check in online, they need copies of the signed docs. Also, if you booked any excursion outside
DCL, your email confirmations.
Laundry soap and dryer sheets
Ziplock bags - you will be packing wet bathing suits after CC and it keeps everything else dry.
Laundry bag - I have several mesh laundry bags and use one of those to keep dirty laundry in. A suitcase works as well.
Reading material - it is pricey on the ship - but only list price.
Dollar bills - for tipping room service
Pepsi and beer - we always stop and pick up a 12 pack of each
Thank-you cards - if we have an over the top room steward, server etc. I write them notes and put their tip in there.
Space in your luggage to bring home FE gifts and souvenirs
Well, that is all I can think of now. I don't know if you are using DCL transportation or renting a car but if you have your own transportation, you could stop at the store on the way and pick some of this up before you board. With the exchange rate, some of this may be less expensive for you here than in Canada. With having to pay for your luggage, it isn't worth the extra bag maybe. Also, remember that you can ship a box to the port.