get_youtube_subscription_rss_feeds.user

// ==UserScript==
// @name        [disable when not needed] YouTube - Get all subscribed channels' RSS feed URLs
// @namespace   localhost
// @description Gets all the channel IDs that you're subscribed to and makes RSS feed links out of them
// @include     https://www.youtube.com/feed/subscriptions*
// @version     1.0
// @grant       none
// ==/UserScript==

/* TO USE THIS SCRIPT:
 * 1. Add it to GreaseMonkey.
 * 2. While logged in on YouTube, visit this URL:
 *    https://www.youtube.com/feed/subscriptions
 * 3. The list will pop up in an alert box.  Select it all, and copy/paste it
 *    into your favorite text editor
 * 4. ???
 * 5. PROFIT!
 */

// this selector is carefully chosen to gloss over the fact that the channels
// can be split into two lists depending on the number of channels you're
// subscribed to and the vertical height of your browser window
var sublist = document.querySelectorAll( '#guide-subscriptions-container li.guide-channel a.guide-item' );
var i, channelRSS = new Array( sublist.length );
var RSSbase = 'https://www.youtube.com/feeds/videos.xml?channel_id=';
for( i = 0; i < sublist.length; i++ ) {
 channelRSS[i] = sublist[i].getAttribute( 'title' ) + ' - ' + RSSbase + sublist[i].getAttribute( 'data-external-id' );
}
alert( channelRSS.join( '\n' ) );