Figures and Tables in multicol
If you use \begin{figure} ... \end{figure} in a multicols environment, the figure won't appear. If instead you use \begin{figure*} ... \end{figure*} the figure will stretch right across the page, probably at the top of the page
It's possible to have single-column figures and tables with captions, but you might have to fiddle with the placement because they won't 'float'. Put the following before \begin{document}
\makeatletter \newenvironment{tablehere} {\def\@captype{table}} {} \newenvironment{figurehere} {\def\@captype{figure}} {} \makeatother
then use figurehere and tablehere where you'd normally use figure[h....] and table[h...]