You should carry everything you need and nothing more.
Finding that fine line can be tricky, but here are some basics.
Always carry identification. You probably want keys and maybe a phone. You may want sunscreen, Chap Stick, and a snack. Do not forget food for a longer ride. You should have some money with you for food, or emergencies.
You should always be prepared for a flat tire. Add a few tools and you can fix many problems on your bike. See our February newsletter for details on this. A map can be quite handy. It can give you the confidence to explore somewhere new.
It is good to be prepared for weather. Knee warmers, arm warmers, toe covers, and a wind vest are all fairly small. In cooler months you may want to add more clothes including extra gloves and a jacket.
Oh yes, always be prepared for a flat tire!