Sunscreen is a must. A good hat, and sunglasses. A raincoat, that rolls up to fit in a small pack. A small pack to carry your great tiny digital camera and refillable, reusable water bottle (make sure its stainless steel!) Some yummy, healthy energy snacks. Lots of karabiners so you can attach all your stuff to your pack.
Yes I know I look like a complete touristy dork, but the sparkly sweater gets me a little style street cred.Other important and necessary items you can carry in your tiny pack.
A packet of tissues, for bathrooms with no t-paper, (a tip I picked up in Asia),
baby wipes, for the night after camping in a tent with nowhere to wash, (picked up at burning man),
insect repellent, to avoid bites but just in case, tiger balm, to relieve itching, calamine lotion,
and my special mix of lavender and aloe for sunburns
oh and tweezers and nail clippers!!!