Be seen: lights
For your own and others’ safety, you should buy bicycle lights. Using lights during daytime reduces the cyclists’ accident rate by 19%, according to a Danish study.
You usually look for a white light at the front and a red light at the back. Most lights are rechargeable nowadays, so you won’t have to bother buying alkalines every now and then. You can choose your light by the amount of light they produce (in Lumens) and their beam pattern (the beam width).
Again, you can get good advice asking you local bike shop.