Adapted from my answer at raster graphics, here using .85cm grid size with .5pt, black border thickness.
\documentclass{article}
\usepackage[usestackEOL]{stackengine}
\usepackage{xcolor, graphicx}
\newsavebox{\Bbox}\newsavebox{\Gbox}
\def\thk{.5pt} % RULE THICKNESS
\def\gsize{.85cm} % GRID SIZE
\def\bordercolor{black} % GRID BORDER COLOR
\def\coresize{\dimexpr\gsize-2\dimexpr\thk}
\setstackgap{S}{-\thk}
\def\Grid#1{\kern-\thk\fboxsep=0pt\relax\fboxrule=\thk\relax%
\textcolor{\bordercolor}{\fbox{\textcolor{#1}{\rule[-.5\coresize]{\coresize}{\coresize}}}}}
\newcommand\Cgeneric[2][]{\stackinset{c}{.0pt}{c}{-.4pt}{$#1$}{\Grid{#2}}}
\newcommand\Cw[1][]{\Cgeneric[#1]{white}\ignorespaces}
\begin{document}
\begin{table}
\centering
\caption{My caption}\smallskip
\Shortstack{%
\Cw[x^2] \Cw[x_2]\\
\Cw[\overleftarrow{ba}] \Cw[\alpha]\\
\Cw[\overbrace{ab}] \Cw[\Gamma]\\
\Cw[\underbrace{ab}] \Cw[\beta]\\
\Cw[\Longleftrightarrow] \Cw[\gamma]
}
\end{table}
\end{document}

By using the color facility of the cited answer, with a cell size of 1cm and broadening the border thickness to .75pt with a color of black!50...
\documentclass{article}
\usepackage[usestackEOL]{stackengine}
\usepackage{xcolor, graphicx}
\newsavebox{\Bbox}\newsavebox{\Gbox}
\def\thk{.75pt} % RULE THICKNESS
\def\gsize{1cm} % GRID SIZE
\def\bordercolor{black!50} % GRID BORDER COLOR
\def\coresize{\dimexpr\gsize-2\dimexpr\thk}
\setstackgap{S}{-\thk}
\def\Grid#1{\kern-\thk\fboxsep=0pt\relax\fboxrule=\thk\relax%
\textcolor{\bordercolor}{\fbox{\textcolor{#1}{\rule[-.5\coresize]{\coresize}{\coresize}}}}}
\newcommand\Cgeneric[2][]{\stackinset{c}{.0pt}{c}{-.4pt}{$#1$}{\Grid{#2}}}
\newcommand\Cw[1][]{\Cgeneric[#1]{white}\ignorespaces}
\newcommand\Ct[1][]{\Cgeneric[#1]{brown!40!gray!40}\ignorespaces}
\newcommand\Cb[1][]{\Cgeneric[#1]{cyan!30}\ignorespaces}
\begin{document}
\begin{table}
\centering
\caption{My caption}\smallskip
\Shortstack{%
\Cb[x^2] \Cb[x_2]\\
\Cw[\overleftarrow{ba}] \Ct[\alpha]\\
\Cw[\overbrace{ab}] \Ct[\Gamma]\\
\Cw[\underbrace{ab}] \Ct[\beta]\\
\Cw[\Longleftrightarrow] \Ct[\gamma]
}
\end{table}
\end{document}

SUPPLEMENT
At the OP's request, here is a version that allows independent setting of the cell height and width, via \gheight and \gwidth:
\documentclass{article}
\usepackage[usestackEOL]{stackengine}
\usepackage{xcolor, graphicx}
\newsavebox{\Bbox}\newsavebox{\Gbox}
\def\thk{.75pt} % RULE THICKNESS
\def\gheight{0.65cm} % GRID SIZE
\def\gwidth{1cm} % GRID SIZE
\def\bordercolor{black!50} % GRID BORDER COLOR
\def\coreheight{\dimexpr\gheight-2\dimexpr\thk}
\def\corewidth{\dimexpr\gwidth-2\dimexpr\thk}
\setstackgap{S}{-\thk}
\def\Grid#1{\kern-\thk\fboxsep=0pt\relax\fboxrule=\thk\relax%
\textcolor{\bordercolor}{\fbox{\textcolor{#1}{\rule[-.5\coreheight]{\corewidth}{\coreheight}}}}}
\newcommand\Cgeneric[2][]{\stackinset{c}{.0pt}{c}{-.4pt}{$#1$}{\Grid{#2}}}
\newcommand\Cw[1][]{\Cgeneric[#1]{white}\ignorespaces}
\newcommand\Ct[1][]{\Cgeneric[#1]{brown!40!gray!40}\ignorespaces}
\newcommand\Cb[1][]{\Cgeneric[#1]{cyan!30}\ignorespaces}
\begin{document}
\begin{table}
\centering
\caption{My caption}\smallskip
\Shortstack{%
\Cb[x^2] \Cb[x_2]\\
\Cw[\overleftarrow{ba}] \Ct[\alpha]\\
\Cw[\overbrace{ab}] \Ct[\Gamma]\\
\Cw[\underbrace{ab}] \Ct[\beta]\\
\Cw[\Longleftrightarrow] \Ct[\gamma]
}
\end{table}
\end{document}
