Is there a way to pass variables into templates in Meteor?

All of the previous answers are overkill or outdated. Here’s how you can pass static parameters into templates, directly from HTML+Spacebars code, as of Meteor 0.8.x:

<div class="slot-wrapper">
  {{> slot number="1"}}
  {{> slot number="2"}}
  ...
</div>

<template name="slot">
  <div class="number"><span>{{number}}</span></div>
</template>

All you have to do is pass key="value" parameters in the {{> template}} inclusion call:

{{> slot number="1"}}

Learn more at Spacebars Secrets: Exploring Meteor Templates.

If you want to pass the caller template’s data to the child/nested/called template, here’s how to do it: pass nothing. Instead, from the nested template, access the parent data context, ../:

<div class="slot-wrapper">
  {{> slot number="1"}}
  {{> slot number="2"}}
  ...
</div>

<template name="slot">
  <div>Machine name: {{../name}}</div>
  <div class="number"><span>{{number}}</span></div>
</template>