Change Section titles to Small Caps only in ToC

Optimal Solution

Load the tocloft package and put \renewcommand{\cftsecfont}{\scshape} after it in the preamble. MWE:

\documentclass[11pt]{article}
\usepackage{tocloft}
\renewcommand{\cftsecfont}{\scshape}
\begin{document}

\title{My document}
\maketitle

\tableofcontents

\section{first section}
bla

\subsection{a subsection}
bla

\section{second section}
bla
\end{document}

This will only change the TOC, not your headings.

Subpar solution

If, for any reason, you cannot load tocloft, this is the ugliest hack ever:

% make your sections using \newsection{title}

\newcommand{\newsection}[1]{
\stepcounter{section}
\section*{\arabic{section}. #1}
\addcontentsline{toc}{section}{\scshape \arabic{section}. #1}
}

Just for comparison, here's a solution using the titletoc package, the important part is

\titlecontents{section}
[0pt]                                               % left margin
{}%
{\contentsmargin{0pt}                               % numbered entry format
    \thecontentslabel\enspace%
    \large\scshape}
{\contentsmargin{0pt}\large}                        % unnumbered entry format
{\titlerule*[.5pc]{.}\contentspage}                 % filler-page format (e.g dots)
[]                                                  % below code (e.g vertical space)

I loaded the hyperref package just for demonstration.

Here's a complete MWE to play with.

% arara: pdflatex

\documentclass{article}
\usepackage{titletoc}
\usepackage{hyperref}

\titlecontents{section}
[0pt]                                               % left margin
{}%
{\contentsmargin{0pt}                               % numbered entry format
    \thecontentslabel\enspace%
    \large\scshape}
{\contentsmargin{0pt}\large}                        % unnumbered entry format
{\titlerule*[.5pc]{.}\contentspage}                 % filler-page format (e.g dots)
[]                                                  % below code (e.g vertical space)


\begin{document}

\tableofcontents
\loop
\section{Section text}
\ifnum\value{section}<5\repeat

\end{document}