A few things that are easy to forget, but invaluable when you remember them.
Address Book Just For Travel - Don't take your normal address book - get a little one and add the people you'll want to send postcards to. You can also add all your new friends as you travel. If you loose the book, it won't mean loosing all your contacts.
Lint Brush Substitute - Instead of a lint brush, pack several of those clear plastic, adhesive airbill pouches used for Federal Express packages. They're flat, light and disposable, and they work very well.
Empty Film Containers, Sewing Thread - Collect empty film-containers!!! They are SO useful. I've collected them, and then I use them to bring small amounts of pins/safety pins, hair clips, yes - even TOOTHPASTE! The containers keep the items dry and safe. (Toothpaste will keep fresh.) Also, rolls with bills and coins fit into the containers. Before traveling be sure to bring some thread in the same colors as your clothes; take a small piece of cardboard and wrap the thread around it. Keep extra buttons, needles and thread in an empty film container. This will always be handy to have, for small repairs.