WordPress RSS feed widget displays feed entries in chronological order.
But some times it is better to display the entries in the order they appear in feed.
For example Popular books of the week.
To do so, make below changes to core wordpress.
Filename = feed.php
function = fetch_feed()
before $feed->init add below line:
ps: It is bad idea to change core wordpress. Until you find a plugin it is a quick fix.