Essential Cycling Accessories
Once you have your new bike, you will need a few accessories to make your new hobby more enjoyable.
Water Bottle Holder and Water Bottle
You will need to hydrate before, during, and after your ride. Get at least one water bottle with a holder. Water bottles come in small and large sizes. The holders, called "bottle cages" or just "cages" are commonly made of aluminum, plastic or carbon fiber.
Rear Seat Bag
You will need a bag to carry a spare tube, your keys, phone, sunblock, medications or whatever else you might need.
Bike Pump for the House
You need a good floor pump to keep in your house or in your car on long bike trips. These are larger pumps with long pump cylinders that will pump higher pressures and more volume in less pump strokes. Bicycle tubes are porous and they will lose a little air every day until they are nearly flat even when they don't have a puncture. You should check your tire pressure before every ride.
Bike Pump for Your Bike
You need a good portable bike pump to carry on your bike or perhaps in the seat bag. These pumps are smaller and lighter than floor pumps and they take much more effort and many strokes to fill a tube and tire to proper pressure. They are however, indispensible in case of emergency.
Spare Bike Tube
Put a spare tube in your rear seat bag. If you get a flat tire, take out the old flat tube and put in the seat bag for patching at a later time. Check the tire and clear out any shark object that may have punctured the original tube. Put the new spare tube in the tire, pump it up with your portable bike pump and carry on with your ride.
Bike Tire Levers
These are little plastic levers to help get the tire off and off the rim when replacing inner tubes. Plastic levers are very common, but there are metal ones available as well. Plastic is supposed to help prevent damaging / puncturing the new tube while it's being installed. Have someone show you how to use these things if you haven't used them before.
Protect your head from serious injury. Get a helmet. Like anything you have to wear, you need to try on several to find one that is comfortable and fits well.
Gloves will keep your hands comfortable and prevent callouses. They will also help prevent your hands from getting skinned up if you crash and use your hands to break your fall.
Other accessories to consider are an odometer / speedometer, a bike rack for your car, a kickstand for parking your bike, a good lock, and lights for safety in low light riding conditions.