Ok i know the solution for this is likely very simple, and i couldnt seem to find a solution after searching around so here goes:

I see the general trend is to create an rss feed for each document type, like news, articles, announcements, events etc. But that would be overkill on my site, and i want a feed that can show entries for two different document types at the same time.

I am using the bog standard RSS feed template built into umbraco, i have pasted the code in below which works just fine, but like i said, needs to support one or more document types:

<xsl:param name="currentPage"/>

  <!-- Update these variables to modify the feed -->
  <xsl:variable name="RSSNoItems" select="string('10')"/>
  <xsl:variable name="RSSTitle" select="string('cuvkbh.dk')"/>
  <xsl:variable name="SiteURL" select="string('http://www.cuvkbh.dk')"/>
  <xsl:variable name="RSSDescription" select="string('Seneste nyheder og aktiviteter')"/>
  <xsl:variable name="rootNode" select="umbraco.library:GetXmlNodeById(1048)"/>


  <!-- This gets all news and events and orders by updateDate to use for the pubDate in RSS feed -->
  <xsl:variable name="pubDate">
    <xsl:for-each select="$rootNode/* [@isDoc]">
      <xsl:sort select="@createDate" data-type="text" order="descending" />
      <xsl:if test="position() = 1">
        <xsl:value-of select="updateDate" />
      </xsl:if>
    </xsl:for-each>
  </xsl:variable>

  <xsl:template match="/">
    <!-- change the mimetype for the current page to xml -->
    <xsl:value-of select="umbraco.library:ChangeContentType('text/xml')"/>

    <xsl:text disable-output-escaping="yes">&lt;?xml version="1.0" encoding="UTF-8"?&gt;</xsl:text>
    <rss version="2.0"
    xmlns:content="http://purl.org/rss/1.0/modules/content/"
    xmlns:wfw="http://wellformedweb.org/CommentAPI/"
    xmlns:dc="http://purl.org/dc/elements/1.1/">

      <channel>
        <title>
          <xsl:value-of select="$RSSTitle"/>
        </title>
        <link>
          <xsl:value-of select="$SiteURL"/>
        </link>
        <pubDate>
          <xsl:value-of select="$pubDate"/>
        </pubDate>
        <generator>umbraco</generator>
        <description>
          <xsl:value-of select="$RSSDescription"/>
        </description>
        <language>da</language>

        <xsl:apply-templates select="$rootNode/descendant-or-self::NewsItem[@isDoc and string(umbracoNaviHide) != '1']">
          <xsl:sort select="@createDate" order="descending" />
        </xsl:apply-templates>
      </channel>
    </rss>

  </xsl:template>

  <xsl:template match="* [@isDoc]">
    <xsl:if test="position() &lt;= $RSSNoItems">
      <item>
        <title>
          <xsl:value-of select="@nodeName"/>
        </title>
        <link>
          <xsl:value-of select="$SiteURL"/>
          <xsl:value-of select="umbraco.library:NiceUrl(@id)"/>
        </link>
        <pubDate>
          <xsl:value-of select="umbraco.library:FormatDateTime(@createDate,'r')" />
        </pubDate>
        <guid>
          <xsl:value-of select="$SiteURL"/>
          <xsl:value-of select="umbraco.library:NiceUrl(@id)"/>
        </guid>
        <content:encoded>
          <xsl:value-of select="concat('&lt;![CDATA[ ', ./bodyText,']]&gt;')" disable-output-escaping="yes"/>
        </content:encoded>
      </item>
    </xsl:if>
  </xsl:template>