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.
Luggage and bags:
Bring a daypack and load it with a couple bottles of water and some delicious sandwiches from a local snack bar...then find a spot while hiking the trail and enjoy a scenic lunch!
Clothing/Shoes/Weather Gear: I highly recommend a good pair of trekking shoes for the trail between the 5 towns. There are lots of slopes, stairs, and rocky crossings. If the trail is at all wet the rocks are EXTREMELY slippery. A good pair of shoes can make all the difference.
comfortable shoes , swimsuit and towel to go swimming at Monterrosso
Toiletries and Medical Supplies: dramamine if u get seasickness easily and you are going to take a boat
Photo Equipment: Bring lots of film!!! Very beautiful, the pics do not do it justice