You can get any adult bike and a wide range of cycling equipment and clothing. You can select cycling equipment with a bike, or if you are already have a bike and are cycling to work you can choose to get equipment only, with all the same tax savings.
As a guide any items which help make you safer, keep your bike safe, or help with your commute can be included except for:
Computers, including GPS units
Training equipment, such as turbo trainers and energy food and drink