I don’t know Emacs, but I know a way to do that in Vim, and Emacs might support a similar method. In Vim, Ctrl-A and Ctrl-X increment and decrement the number the cursor is over. You can generate a list by recording a macro that duplicates the current line and then increments its number (qqVyp ^a q), and running that macro repeatedly (10@q). Emacs might also have a function for incrementing characters, not just numbers.