\documentclass[boxit]{jacow}
\usepackage{lipsum}
\usepackage{stfloats}

\listfiles
%\fnbelowfloat
%\fnunderfloat
\begin{document}

\title{How to place Double-column floats on the first page of an article in twocolumn mode\thanks{Funded by \TeX.StackExchange}}
\author{V. RW Schaa\thanks{v.r.w.schaa@gsi.de}, GSI, Darmstadt, Germany}

\maketitle
\begin{abstract}
\lipsum[1]
\end{abstract}

\section{More of the same}
\lipsum[3]

\lipsum[17]

\begin{table*}[h!b]
	\centering
	\caption{This Is to Show How Double-Column Tables (and Figures) Can Be Placed at the Bottom of the First Page}
	\begin{tabular}{ccccc}
		\toprule
		 \bfseries Cell R/C	&  \bfseries Cell R/C	&  \bfseries Cell R/C	&   \bfseries Cell R/C	&   \bfseries Cell R/C	\\
		  \midrule
		Row 1 - Column 1 & Row 1 - Column 2 & Row 1 - Column 3 & Row 1 - Column 4  & Row 1 - Column 5 \\
		Row 2 - Column 1 & Row 2 - Column 2 & Row 2 - Column 3 & Row 2 - Column 4  & Row 2 - Column 5 \\
		\bottomrule
	\end{tabular}
\end{table*}

\section{Now something completely different}
\lipsum[5]

\begin{table*}[t]
	\centering
	\caption{This Is More the Standard -- Double-Column Tables Appearing at the Top of the Second Page}
	\begin{tabular}{ccccc}
		\toprule
		 \bfseries Cell R/C	&  \bfseries Cell R/C	&  \bfseries Cell R/C	&   \bfseries Cell R/C	&   \bfseries Cell R/C	\\
		  \midrule
		Row 1 - Column 1 & Row 1 - Column 2 & Row 1 - Column 3 & Row 1 - Column 4  & Row 1 - Column 5 \\
		Row 2 - Column 1 & Row 2 - Column 2 & Row 2 - Column 3 & Row 2 - Column 4  & Row 2 - Column 5 \\
		\bottomrule
	\end{tabular}
\end{table*}

\lipsum[7-10]

\end{document}