1. Rohirrim are mostly vegetarian. Basis: In the LotR movies, Jackson didn't include any real meat sources on the Rohan sets (easy to overlook, I know) and it gave me an Idea.
2. Rohirrim are mostly areligious. On the set there was no real religious structures. Plus they're busy with horses.
3. Theoden's unnamed sisters are Swanhild, Sexburg, and Noniel. I use this in my rp and fanfic. Swanhild died as a child, usually.
4. Due to a letter published in X-men asking how old Gambit and Rogue were (the answer was late teens/early twenties), my headcanon for Gambit is that he's actually quite young and was sixteen when he married Belladonna. This, I feel, explains a lot of his fuck ups.
5. Speaking of Gambit, going by the X-Men: The End alternate universe comic, I've decided to go with Gambit being the clone of Cyclops and Sinister for main canon.
Note: With the X-Men ones, I know I've probably been contradicted already because the comics universe is constantly adding onto itself, eating itself, and completely contradicting itself. Given I don't read the comics anymore (they literally put every character I liked on a bus and blew the bus up), I'm pretty comfortable going off into my own mental territory. What I'm saying is, 'because I want to' is the answer for any arguments about the X-Men ones. The Rohirrim ones, I'm open to info.