\documentclass{article}
\newcounter{num}
\newenvironment{varlist}[2]
   {\begin{list}{\textrm{#1 #2{num}:}}{\usecounter{num}%
       \setlength{\labelsep}{5mm}
       \settowidth{\leftmargin}{\textrm{#1 #2{num}:}}
       \addtolength{\leftmargin}{1cm}}}
   {\end{list}}
\begin{document}
\noindent Previous outer text
\begin{varlist}{Sample}{\Alph}
   \item without any value
   \item with an enclosed voucher
\end{varlist}
\end{document}
 
