If you read enough Han and Leia fanfic - and sometimes even if you only read a little bit - you will come across certain recurring elements that have no blatant reason for us to believe them to be true based on what we see in the movies, but it just seems that collectively the Han and Leia community believes them to be fact. Of course with any of these, there are exceptions. But here are a few examples of things that always seem to pop up:
1. Leia can't cook. Seriously, I don't think I've ever read a fanfic in which Leia whips up a five-course meal for her and Han. Why do we all believe this to be true? In the entirety of the movies, she never even eats let alone has the opportunity to cook anything. I suppose having grown up a princess we could all infer that she always had her meals prepared for her and skipped learning how to cook anything decent. Who are we to say that part of her privelaged upbringing didn't include training from the finest culinary artists in all of Alderaan? But none of us seem to believe that. So, in every story I've ever read in which Leia enters the kitchen, other characters in the story get very nervous...
2. Han didn't have a stable home life growing up. Whether you subscribe to the back story put forth by the Han Solo trilogy or not, it seems that we are all in agreement that Han's parents were no Ward and June Cleaver, even if he did know who they were. Whether he was orphaned and has no idea what happened as is written in the "official" version, or maybe his family was killed when he was a bit older and he remembers it, we seem to have decided that he wasn't the kind of kid who was tucked in every night by his mommy and daddy and played smashball on the local little league team. I'm sure most of us have read versions of his story in which his parents or at least one or the other are still alive and he chooses not to talk to them, but I think we are all in agreement that after he got the medal for helping blow up the Death Star he didn't call his parents to tell him about the new chick he met.
3. Leia is a virgin. Ok, this one isn't completely universal. But I think it is at least generally accepted to be truth. There is that "popular" Leia-was-raped-on-the-Death-Star theory, but it is not one I have ever really subscribed to. When Luke finds her, does she look like the type of girl who was recently raped? Forget the fact that she doesn't particularly look like the type of girl who just saw her entire planet blown up, either. Maybe it's the fact that she wears white all the time or fights her feelings for Han so adamantly, but for the most part, we don't read about a Leia who slept with a few boys back in University.
4. Han is definitely not a virgin. This one almost goes without saying. Do we need a reason? He's Han freaking Solo. Plus, he's a hot guy in his early 30's. How could he possibly not have been getting some action before? Although once upon a time I did read a story, which unfortunately I can't find anymore and don't know the name of, in which Han was the virgin and Leia was the experienced one. It didn't get into all of the fun details, but it did have Leia finding out about his inexperience and offering to take him to his cabin and "show him the ropes" so to speak. But honestly, I don't think anyone sees that as a possibility.
5. If anyone is cheating on anyone, it's Leia cheating on Han. I'm not a big fan of stories that involve cheating and I'm not a fan of cheating in real life. I don't get it. You want to sleep around? Fine. Just make sure that anyone you're involved with knows up front so you're on the same page. But if a fanfic writer must put some cheating into a story, it is almost exclusively Leia cheating on Han. Or another man vying for Leia's affections, such as Isolder. I can recall one story in which it even alluded to the possibility of Han cheating on Leia, and in the end he couldn't go through with it. I don't see either one of them cheating in the first place, but I'm not sure why everyone always sees Leia as the one being unfaithful. Is it because we can see Han forgiving her but not the other way around? Because if a man cheats, he's just a horrible person and doesn't deserve another chance but a woman does? I don't know, but that's the way it always seems to go.
So there are five of them, anyway. I'm sure there are more and feel free to add if there are any you feel I've left out. There's another possibility I had thought of, but not sure how to put it delicately. It has to do with rumors of certain Corellian, um, attributes, maybe? Ones that would be greatly in Leia's benefit. That's all I'm going to say about that.