I see no snacks on your list.
A Power Bar or similar (perhaps two of these). A banana (stuffed in the back of your shirt jersey??
I can't ride without a sweat band, and, in fact, carry 3, one on my head and two wrapped around the seat post.
Any chance of cold or rain?
Sun Screen?
Clothing is at your option. I have seen everything, including a whole group of guys riding with Tuxedos on. You will likely be more comfortable in a pair of bike shorts and a Jersey, but they certainly are not required.
I generally carry some pain-killer, string, duct tape, needle (I use a 35 mm plastic cannister for items such as these) and soome basic tools. But, these are not necessary. I am generally the "everything but the kitchen sink" kind of guy, anyway.
Hey - have a lot of fun and enjoy yourself. It is a great experience.