There is an old trick from Dos days (still valid in all windows under cmd prompt or even command.com) when we wanted to create a quick file without loading up edit (edit.com) was to use copy con. The exact syntax is:
copy con filename

Subsequent lines you type are copied to the file. You could end the content by pressing Ctrl-Z and then pressing Enter.

Good old days :)

My other favorite trick was marking directories as hidden and system so others couldn't access it, especially useful in shared computers.

What are your favorite DOS tricks?