I suppose most of my stuff isn't considered especially odd after reading previous replies. We typically will bring baggies, magnets, laundry detergent, snacks, etc. I take my pillow anytime we travel. I use a down pillow so it smashes down in my suit case no problem.
But the oddest thing I bring is 12x12 scrapbooking envelopes so I can sort items I collect for my scrapbooks. Each port has its own folder; they usually have items in them when we board from my research before hand. And I bring a notebook so I can journal each day and put in said folders. By doing this most of my stuff is organized when I get home. Makes scrapbooking our adventures so much easier. (I do this for land based vacations also)