As I watched my husband and daughter pack for a camping trip this past weekend, I noticed a couple of items I will be sure to bring on future trips to Spain (or anywhere else in Europe):
Campsuds soap--this stuff comes in small bottles, is highly concentrated (and environmentally friendly), and can be used for hands and body, hair, clothes, dishes, whatever. I think I will keep some in my day pack for washing utensils (see next item below), some clothes, and even hands when there's not soap in a restroom.
Strong plastic utensils--these cost about $1 a set at camping supply stores, and the knives really cut. I would have taken metal ones, but I feel strange packing a metal knife just now!! They are meant to be washed and reused...great for yogurt, fruit, or bread from the grocery store.
Small stuff sacks--these little nylon or mesh bags are great for organizing your suitcase or backpack.
People have already mentioned flashlights, of course.
Happy packing!