When you export a module you get a file called "common.xml" that contains all of the information that goes into the equipment lists. There is a section called lists that you can edit/create to make one. First you need to tell it you want an equipment list, so in the example below you'll see a section called "equipmentlists" with an example list called Adventuring Gear. Now that you've referenced your Adventuring Gear category, you need to create a list of items. Below you see a "record name" called lists.equipment.gear. That means we need to make a "gear" section underneath lists, but also within equipment. Another thing is you'll notice in my below example references to "id-00066". That is the "id" for arrows in my example below and it matches the id number for arrows that comes from the item list (as it must exist as a separate item) and will be shown in the <item> section of common.xml. The same id number is also in the <equipmentdata> section of the common.xml file. Obnoxious, but thats what gets "arrows" placed into all of the appropriate places. I have added those bits in the example what that looks like for my "arrows" example so there's a complete sample. This is all work I had to do to import Adventures in Middle Earth to FG so maybe is a bit much, but does show what it looks like.
Here is what it would look like:
<lists>
<equipment>
<equipmentlists>
<name type="string">Equipment</name>
<index>
<r01gear>
<name type="string">Adventuring Gear</name>
<listlink type="windowreference">
<class>reference_adventuringgeartable</class>
<recordname>lists.equipment.gear</recordname>
</listlink>
</r01gear>
</index>
</equipmentlists>
<gear>
<description type="string">Adventuring Gear</description>
<groups>
<r01ammunition>
<description type="string">Ammunition</description>
<equipment>
<id-00066>
<link type="windowreference">
<class>reference_equipment</class>
<recordname>reference.equipmentdata.id-00066</recordname>
</link>
<name type="string">Arrows (20)</name>
<cost type="string">1s</cost>
<weight type="number">1</weight>
</id-00066>
</r01ammunition>
</groups>
</gear>
</equipment>
<referencemanual>...stuff here...</referencemanual>
<imagewindow>...stuff here...</imagewindow>
<item>
<name type="string">Items</name>
...65 other items above this one...
<id-00066>
<listlink type="windowreference">
<class>item</class>
<recordname>reference.equipmentdata.id-00066@Adventures in Middle Earth Player's Handbook</recordname>
</listlink>
<name type="string">Arrows (20)</name>
</id-00066>
...other items follow...
</item>
...bunch of other sections follow (npc, backgrounds, class, feat, race, skill)
</lists>
<reference static="true">
...bunch of data sections...
<equiptmentdata>
<category name="AiME - PHB" baseicon="0" decalicon="0">
...65 other items above this one...
<id-00066>
<ac type="number">0</ac>
<bonus type="number">0</bonus>
<cost type="string">1s</cost>
<description type="formattedtext">
<p></p>
</description>
<isidentified type="number">1</isidentified>
<istemplate type="number">0</istemplate>
<locked type="number">1</locked>
<name type="string">Arrows (20)</name>
<subtype type="string">Ammunition</subtype>
<type type="string">Adventuring Gear</type>
<weight type="number">1</weight>
</id-00066>
...other items follow...
</equipmentdata>
...even more data sections...
</reference>