Sunglasses
Sunglasses will keep the sun out of your eyes and protect them from its harmful rays. They can also help keep wind or precipitation out of your eyes. The best sunglasses will be lightweight and have ample UV protection. Interchangable lenses will give you the most flexibility.
Baseball cap
A baseball-style cap with a visor will provide protection from the sun as well as shielding your face from lighter precipitation. For best results, try a lightweight breathable hat designed to hold up against the rain, snow, and perspiration.
Long-sleeved shirt
When the weather is cooler a long-sleeved shirt is ideal. Technical fabrics are a must for keeping the sweat off your skin.
Light jacket
A light jacket over a long-sleeved shirt on cold days will keep you just warm enough. Your best option will be something wind and waterproof, as well.
Shorts
A nice pair of shorts is crucial for most temperatures and conditions. A built-in liner to reduce chafing and keep you comfortable is helpful. And something made from a technical fabric or nylon will be light and comfortable. Stay away from cotton here if you can! And it wouldn't hurt to ensure they have some reflective areas!
Lightweight gloves
A pair of thin gloves will provide just enough warmth for cool temps. Those made with technical fabrics are best, and will do a good job of wicking away sweat. They'll also be easy to stash in a pocket if they end up not being needed.
Sunblock
Prevent sunburn and exposure to harmful UV rays by getting some sunblock -- ideally one with a 30 SPF rating or higher.
Reflective gear
Make sure you can be seen at night! Try to wear clothing with reflective surfaces, or get a special reflective vest or wearable LED blinking lights. You're much harder to see at night than you think!
Identification
It's always a good idea to be prepared for possible trouble. Keep some ID on you in case the worst happens. Throw your license or business card in your back pocket, or better yet -- use something like a RoadID that can also contain additional vital information if you're in trouble.
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