Here is my list of easy to forget items. They are all small and shouldn't take up much room. I left out all the easy to remember stuff.
Reservations/Contact list - Address book/preaddressed labels (Possible cell phone)
Sleep Aid, Inflatable pillow, Eyeshades, Ear plugs
Laundry Soap, Chamois, Clothesline, Spot Remover, Fabreeze
Lock – Backpacker, Cable-lock or both
Shave kit items - Chapstick, Bug Repellent, Sunscreen, Kleenex, Floss, Nail-clippers, Mirror
Daypack items - Swiss Army Knife (buy there), Plastic Fork, Monocular, Small LED Flashlight, Mini-Tripod, Band-aids, Sewing Kit, Duct Tape, Safety Pins.
General items - Journal, Pens and Gluestick (possible digital voice recorder), Multiple Zip-Lock bags, Digital Camera with large memory on neck strap w/whistle, GPS
Convertible Carry On -Throw in a couple of dryer sheets.
Anything that's on this list can be purchased locally or lived without.