You may take a look at the tabu
package. This extends the well known tabularx
and longtable
so that you can easily handle them both without writing to a aux file.
\documentclass{book}
\usepackage{tabu}
\usepackage{longtable}
% showcase only strip that
% see http://tex.stackexchange.com/questions/50296/problem-with-using-loop-inside-the-tabular-environment
\newcounter{my}
\setcounter{my}{0}
\def\myinsert{}%
\loop\ifnum\themy<100
\addtocounter{my}{1}
\expandafter\def\expandafter\myinsert\expandafter{%
\myinsert
Quite a big cell content & Not so big content but bigger cell \\
}%
\repeat
% end showcase
\begin{document}
\begin{longtabu} to .5\textwidth{X[1]X[2]} % half the width of the text
\myinsert
\end{longtabu}
\end{document}
Any additional information can also be found in the tabu
documentation (texdoc tabu
)