This article is from the Misc Bicycles FAQs, by various authors.
What should you carry?
Rain Jacket or additional clothing depending on the weather and where
the ride is going. If you are climbing a mountain pass, you may need
warmer clothing for the top. Check the weather forecast to determine
if you will also need tights, glove liners, etc. I usually use tights
if the temperature is below 60F, and I carry them if rain is
predicted. In New England, rain can cause the temps to drop
dramatically, and there have been many times that having tights with
me has saved me.
Tools - all the regular stuff, like tubes, tire levers, patch kit,
tire boots*, a foldable tire, chain break tool, spoke wrench,
screwdrivers (phillips and slotted - if your bike uses them), hex
wrenches and adjustable or box wrenches in the sizes necessary for
your bike. As mentioned above, learn how to do minor roadside repairs.
A foldable tire is not an absolute necessity, especially if you are
carrying boots, but it may save time and frustration in event of a
bad cut to the tire or sidewall.
Others tell me that a chainbreak tool isn't necessary. Maybe it's my
tandem background. If you need a chainbreak tool, look for a tandem.
They will have one!
*A tire boot is a 2-3 inch section of old tire with the bead cut off.
If you cut your tire all the way through or cut the sidewall, insert
this between the tube and the tire. This will prevent the tube from
pushing out through the hole and causing more flats. A boot is not
noticeable when riding. Really! (PowerBar wrappers and $20 bills make
good boots too. If you use a $20, you will have the money to buy a new
tire when you get to the bike shop!)
Map or Cue Sheet and a plastic bag to carry it. If the route is
arrowed, you may never have to look at a map or cue sheet. A map is
handy if you get off course for finding your way back on the route. A
plastic bag or map case will keep it dry and readable. Sweat and rain
can make a cue sheet difficult to follow. A handlebar bag will provide
a handy place to keep and read a cue. (For tandems, the captains back
works very well!)
Carry sweatproof sunscreen to be applied during the ride too. Even
the sweatproof stuff comes off during a century.
Padded cycling gloves have been suggested if you don't normally use
Money and Credit Card for food and/or emergencies along the way.
Emergency Contact Info and insurance card. First aid items like baindaids,
neosporin, ibuprofen, and baby wipes might come in handy.