In the installation, when the user is prompted to "Configure the package manager", and answers "No" when asked to add a network mirror, sources.list will not contain any mirror. Although some will learn the link between answering that particular question and the lack of mirror, it isn't obvious.

Later on, when using Kali and when trying to follow tutorials or searching for packages, apt-get won't find anything. It takes a little while to google and figure out what the problem is and it's easy to solve, but it could be easily shortened by adding the mirror, commented out, along with a message explaining why.

It would also be a good idea to improve the message on the installation screen.