Bike frame bag are a convenient and out-of-the-way place to store extra gear on your bike.

Bike frame bag are a convenient and out-of-the-way place to store extra gear on your bike. Bike frame bags can be used in a wide variety of circumstances from local commuting to long distance touring to bikepacking and just about everything in between.
There are three main types of frame bags:
Bike top tube bag: Mounts to your bicycle's top tube and stem or steer tube

Full frame bags: come in a variety of options and mounting styles, and they are often designed to accommodate the huge range of bicycle frame sizes and styles available today. Brands such as Revelate Designs, on the other hand, make full frame bags to perfectly fit the triangles of specific bike models, and maximize the carrying capacity so that racks and panniers are not necessary.

Front frame bags: mount to the front triangle of your bicycle's frame where the down tube and top tube come together.