Sometimes I need to convert a list of lines into a tabular in latex. So I need to add "\\" at the end of each line of the considered region.
To do that use the following trick:
M-% (query replace)
C-q C-j (^J (line feed)) [you need to valid this choice by a carriage return)
\\C-q C-j
So we replace line feed (^J get from C-q C-j) by \\ and a line feed.
Note that carraige return is available via C-q C-m