I tried to combine this answer: https://tex.stackexchange.com/a/73983/4011 with minipage but got an error: ERROR: LaTeX Error: Float(s) lost.
\documentclass{article}
\usepackage{showframe}% http://ctan.org/pkg/showframe
\newcommand{\points}[1]{% Print points in margin
\leavevmode\marginpar{\makebox[\marginparwidth][r]{[#1]}}\ignorespaces}
\reversemarginpar% Points in left margin by default
\begin{document}
\begin{enumerate}
\begin{minipage}[t]{0.5\linewidth}
\item \points{5} This is what a simple open ended question, with no other parts could look like.
\par\vfill
\item This would be where you could put a question with two parts.
\begin{enumerate}
\item \points{2} This would be part~(a).
\par\vfill
\item \points{2} This would be part~(b).
\par\vfill
\end{enumerate}
\item \points{10} This is what a multiple-choice question would look
like.
\par\vfill
\end{minipage}
\begin{minipage}[t]{0.5\linewidth}
Some other text or a picture.
\end{minipage}
\end{enumerate}
\end{document}
Without minipage it works.
Any idea, how to fix this?

minipagedoesn't have a margin, a\marginparinside aminipagewill not work. But what do I know? – Steven B. Segletes Oct 23 '14 at 17:02\marginparuses the\insertmechanism; an\insertdoes something only if it is at the outer level, not inside a box. You may want to look at themarginnotepackage. – egreg Oct 23 '14 at 17:20