Nope. Including an avatar on your profile is not a requirement for you to be able to use Packback -- but it does add a fun twist! If you decide not to create an avatar or would rather create it at a later time, simply skip that step when prompted and your account will appear with a default Packback image in its place.
Once you're ready for an avatar, all you'll need to do is login to your account and click My Account in the upper right-hand corner and then Account Information. A drop-down menu will appear giving you the option to edit your avatar.