Carrying items in a backpack on a bike gets old quickly! Fortunately, there are many different options for places to carry items on your bike. One of the most common ways to add cargo capacity to the bike is to put on a back rack.
You can strap bags on top of the rack or put things in panniers, which are bags specifically designed to latch onto the sides of the rack. A lot of panniers are waterproof to protect your items from the rain. Other common bike cargo options are frame bags for odds and ends, water bottle holders, and handlebar baskets.