Miscellaneous: Although things tend to cool off at night, if you're an American and used to air conditioning, you may find that it is well worth your while to bring a small battery-powered fan with you, or to purchase a slightly larger fan which has the appropriate plug for Italian current. I brought two of the former and we never did get around to buying the latter -- but we certainly would have been much more comfortable had we done so, and at minimal cost.
Miscellaneous: Given the paucity of laundromats -- I never found one -- it is probably wise to bring along a small bottle of laundry detergent (though shampoo will do in a pinch), clothes pins and laundry line. You can wash out your "smalls" each night in the sink, and periodically launder larger items when you have access to a bathtub.
Miscellaneous: Our hotel in Orvieto included bath towels and hand towels, but not what we Americans call "wash cloths" (a small towel used to wash one's face). Luckily, my friend had brought a supply which could be left behind in each city, and I brought Olay's excellent cleansing tissues because that's what I use back in Rhode Island. But if you're younger than we are and dislike using a corner of your bath towel to wash your face, you might think about packing something you wouldn't mind discarding after your visit.
Miscellaneous: A word to the wise: many Italian windows are unscreened. This can come as a very unpleasant surprise in warm weather if you failed to pack insect repellent. Having done so, I did not investigate whether it was available in Italian pharmacies.
Luggage and bags:
If you want to visit Orvieto and stay inside the city and might need to park “outisde” or walk from train/bus stations or from the funicular to your accommodation, I would recomment that you bring luggage on strong wheels or backpacks, they are easier to carry on the often cobblestoned roads.
Clothing/Shoes/Weather Gear: Definitely bring shoes with which you are comfortable for walking. You will walk a lot in Orvieto, and the western part is slightly declined. Streets have cobblestones. Your feet will be grateful in the evening. Bring warm clothes, mainly when you plan to visit any of the underground sights in Orvieto. Umbrella or raincoat might be a good idea, depending on the season. However, as you can see on my photos, in April (2008) it was quite sunny. If you want to visit churches, bring something to cover arms and legs, as you might not be let in with unappropriate clothes.
Toiletries and Medical Supplies: Orvieto has enough pharmacies where you can get medical supply. Bring translation for prescriptions. You might like to bring first aid kits with band-aid, as you might have blisters from walking. Foot cream is a good idea, too. My feet were happy in the evening with this.
Photo Equipment: The most magic impressions in Orvieto is the duomo, both inside and outside. Not to mention the other sights. Make sure you bring a good tele lens and lots of film rolls or memory cards.
Camping/Beach/Outdoor Gear: There is no beach in Orvieto, but Lago Bolsena is near as is Lago di Corbara. Your hotel or agriturismo will most probably have a pool. So swimming suits might be a good idea. If you plan to hike, bring all your equipment, as it is most unlikely to find places where you can rent tents and the other stuff.
Miscellaneous: Binoculars are a good idea for looking at the building details. Maybe a torch as well, in case you might feel uncomfortable when visiting Orvieto’s underground. They are lit, but maybe not enough for someone’s liking.