How to include enumerate in tabular?

Try changing the heading to p{3cm} as shown below:

\documentclass{article}
\begin{document}
\begin{tabular}{|p{3cm}|}
\hline
\textbf{Name:} Foo \\
\hline
\textbf{Main success scenario:} \\ 
\begin{enumerate}
  \item Entry action
  \item next steps\ldots
\end{enumerate}\\
\hline
\end{tabular}
\end{document}

Look at the listliketab package list columns

The following was posted on CTT a long time ago by Donald Arseneau for itemized and enumerated cells

\documentclass{article}
\usepackage{array}
\makeatletter
\newcolumntype{e}[1]{%--- Enumerated cells ---
   >{\minipage[t]{\linewidth}%
     \NoHyper%                Hyperref adds a vertical space
     \let\\\tabularnewline
     \enumerate
        \addtolength{\rightskip}{0pt plus 50pt}% for raggedright
        \setlength{\itemsep}{-\parsep}}%
   p{#1}%
   <{\@finalstrut\@arstrutbox\endenumerate
     \endNoHyper
     \endminipage}}

\newcolumntype{i}[1]{%--- Itemized cells ---
   >{\minipage[t]{\linewidth}%
        \let\\\tabularnewline
        \itemize
           \addtolength{\rightskip}{0pt plus 50pt}%
           \setlength{\itemsep}{-\parsep}}%
   p{#1}%
   <{\@finalstrut\@arstrutbox\enditemize\endminipage}}

\AtBeginDocument{%
    \@ifpackageloaded{hyperref}{}%
        {\let\NoHyper\relax\let\endNoHyper\relax}}
\makeatother
\begin{document}

\begin{tabular}[t]{|i{2.5cm}|e{3cm}|}
\hline
  \item Item A
  \item Item B   &
  \item Item 1
  \item Item 2   \\
\hline
\end{tabular}

\end{document}