In addition to almost all of the above, I carry at least two swivel-necked plastic hangers: great for hanging laundry to dry. (Cheap hotels tend to have wire hangers, and expensive ones tend to have hangers that can't be removed from the closet.) And if you do find yourself in a wire-hanger-only hotel, it's nice to have a decent perch for more fragile items. Also, Woolite and a small sewing kit.

Masking tape has many uses, including emergency repairs of all kinds. I've even used it to hold my camera together when I lost a critical teeny-tiny screw.

Couldn't agree more about carrying extra camera batteries and film. They're usually more expensive in Spain, and if you're in a small town, they may not even be available, especially for you SLR users and slide shooters. Lens tissue is essential, even for point-and-shooters.

A travel iron. Rarely necessary in the U.S. because just about every type of lodging provides an iron and ironing board. But in six trips to Spain, staying in all types of accommodation, I have never found these in my room. (Then again, I've never stayed in an American chain in Spain; maybe they provide them.)

Plastic letter- or legal-size envelopes are ideal for protecting and organizing all the brochures and other papers I tend to collect. Staples sells them in multi-color packs.