Reusable content block

if you’re using ACF, create an options page and then add a field there. Then present that data in a side widget by echoing out the field.

once the field is created you can call it with this code:

<?php the_field('page_content', 'option'); ?>

I like to add it to a function

function rt_show_field() {
    $field = '';
    if (get_field('page_content', 'option')) {
        $field = get_field('page_content', 'option');
    }
  return $field;
}
add_shortcode( 'my-field', 'rt_show_field');

Then if you add that function to your functions.php

you can simply add this short code to a widget

[my-field]

or add the function

echo rt_show_field();

to a template page or whereever you want.