Obviously, in terms of resources available for you to practice your skills and build your demoreel, I cannot skip the fact that I am offering hundreds of exercises for a reasonable price here.

That being said, the best footage you can find and present is the one you create yourself. Filming your own exercises will teach you at least a bit about cameras and lenses if you have the privilege of having a DSLR or similar, and it shows great dedication to your field, as well as giving a very unique look to your demo, making you already stand out from the crowd.

However, if you do not own any camera or fancy smartphone, I compiled a list of footage that I could find, most of them being free to use for your personal training:

Footage:

• ​​​​​​​​​​​​​​​​Arri - ​​Camera Sample Footage & Reference Imag​e​​​​​​
• Blackmagic - Pocket Cinema Camera Gallery
• Blackmagic - URSA Mini Gallery
• ​Blackmagic - Cinema Camera Gallery
• DJI - Ronin 4D Sample footage
• DJI - Inspire 3 Sample footage
• RED - Sample R3D files
• Sony - Venice test footage
• ActionVFX - Practice footage
• Tears of Steel - Movie shots
• ​Peter Timberlake - Practice material​

Elements (those websites are mostly paid resources, yet you will find plenty of elements generously available for free):

• ActionVFX
• FX Elements
• FootageCrate
• Textures.com