This is not a cruise, so packing efficiency is more prized than an extensive wardrobe. A suggested packing list is on the website. Many t-shirts come in the new, high tech wicking fabrics. They are more expensive than cotton t-shirts, but they really do help you feel cooler by removing sweat.
Bike jerseys aren't required, but they're also made from wicking fabrics, and often have up to three pockets on the back to carry snacks, spare inner tubes, cell phones, etc. You know, biker stuff.
Padded bike shorts are strongly recommended for reasons that should be obvious. They also help to keep leg muscles compressed. If you dislike padded shorts, compression shorts are recommended. If you don't like the look of wearing tight bike shorts, mountain bike shorts usually have padded shorts inside a pair of baggy shorts. For women, there are many skirts that have a pair of padded bike shorts hidden underneath.
Pack for layers, so if the weather changes quickly you can add or take off just enough. Augie taught me that you can buy a pair of ladies trouser socks and cut off the seam across the toes to make a colorful pair of arm warmers that are much cheaper (have you had the privilege to meet Augie?) than store-bought arm warmers and they roll up really small when not needed.
Speaking of rolling up, rain gear is most useful if it keeps you warm in a cold rain, but if it you can’t carry it easily with you on your bike, chances are you won’t have it when you need it. Some rain gear packs into its own fanny pack, so you can wear it around your waist when it stops raining. Rain gear should have some reflective trim or logos to help you be seen in poor weather conditions. Likewise, choose rain gear that is visible; yellow or HiViz green instead of fashionable black or navy.
When not raining, suntan lotion actually helps keep you cooler than not wearing it, because it minimizes the UV penetrating your skin and warming it up.
Zip lock baggies are our friends. Pack your clothes in giant ones in your suitcase ... they will help keep your clothes dry in case it rains and they will keep your luggage organized. On your bike, small zip lock baggies can protect cell phones or other essentials from the rain. They also make great map covers in case, you guessed it, it starts to rain.
Padded gloves help to reduce road vibration. Also, if you are bringing a bike that has a straight across handle bar, you really should consider adding bar ends, available at any bike shop. Bar ends provide an optional position for your hands, helping to reduce fatigue in your hands and fore arms.
Bike socks are recommended instead of plain cotton socks for wicking away moisture. aka sweat.