Get category slug and display it on a query_post

Put this code into your function.php

$terms = get_the_terms( $post->ID , 'category');
if($terms) {
  foreach( $terms as $term ) {
    $cat_obj = get_term($term->term_id, 'category');
    $cat_slug = $cat_obj->slug;
  }
}

and then set var $cat_slug into your "choices",

and then set var $cat_slug into your "choices",

$options[] = array(
 "section" => "select_section",
 "id" => WPTUTS_SHORTNAME . "_select_input",
 "title" => _( 'Select (type one)', 'wptuts_textdomain' ),
 "desc" => _( 'A regular select form field', 'wptuts_textdomain' ),
 "type" => "select",
 "choices" => $cat_slug
);

We see from the example that the option accepts a simple array of values:

array( "1", "2", "3")

get_categories returns an array of objects, so we need to do a bit of reformatting to make it work:

$categories = get_categories();
$slugs = array();
foreach( $categories as $category )
    $slugs[] = $category->slug;

Now we have a simple array of $slugs to pass:

$options[] = array(
    "section" => "select_section",
    "id"      => WPTUTS_SHORTNAME . "_select_input",
    "title"   => __( 'Select (type one)', 'wptuts_textdomain' ),
    "desc"    => __( 'A regular select form field', 'wptuts_textdomain' ),
    "type"    => "select",
    "choices" => $slugs
);

I am not positive how to do what you want. But I have been using this framework which is very similar to what you have above but is much easier to use

http://aquagraphite.com/2011/11/smof-documentation/

setting up options is really easy and it is supported through github. There is a place to ask these exact kind of questions. That and the framework has a lot of examples in it that you can copy and paste to get your admin area up and running. I just commented out all the example options so that I could reference them when I wanted to create one of them.

As for your answer. I don't know how to do you but you could try some things like this

"choices" => get_categories(  );