Wearing the right type of clothing can make a big difference in comfort while cycling. While quick jaunts across town may only require a pair of shorts and a t-shirt, you will want a dedicated wardrobe for long distance cycling.
A good place to start is cycling shorts. The tight fitting, mid thigh fit of the common lycra cycling short is a perfect design for pedaling long distances as it reduces wind drag and dries quickly. The most important feature of any cycling shorts is the padding sewn into the seat area of the pants. This will help to provide comfort on long rides and is a very necessary part of your cycling gear.
The next most important piece of cycling clothing is the cycling jersey. These are typically tight fitting, but looser styles are available. Most will have pockets sewn into the rear of the jersey for storing things like spare tubes, bananas or your wallet.
If you are cycling in cool or cold weather, a good cycling jacket is a necessity. This should be wind and waterproof. While aerodynamics are not as important in very cold weather, you will find that a tighter fit will reduce the amount of air drag at higher speeds.
Finally, consider the other two contact points of your bike, the handlebars and pedals. Padded gloves should be used to protect your hands. This dampens the effects of road vibrations, and can protect your hands from injury in the event of a crash. They can also keep your hands warm in cold weather, which is important so that you can maintain control of your bike.
You should consider a good pair of cycling shoes as well. Long distance riders will opt for the stiff soles of a dedicated cycling shoe. These will have provisions on the bottom to attach the cleats necessary for modern pedals. While they are not comfortable to walk in due to their stiff soles, they are a necessary component for those who prefer long distances or competitive riding.