I love putting little stuff in my writing that comes directly from real life. The car the antagonist of my newest book I'm working on, Lady Luck, is a broken down Buick Skylark. That's the car my best friend in high school (and still best buddy) Michael Rubi drove. The passenger side handle wouldn't open the door on the outside of the car, this feature is also present on the car in the book. The book also takes place in the mountains of Colorado (where I was living for the last year up until just recently), so all the places in the novel are are real places I've been with a bit of my imagination thrown in for good measure (basically combining different parts of different cities into one for convenience and theme). There's other things present in there, but those are the biggies I can think of off the top of my head. I do this in most of my books and stories, I dear say in all of them, and I imagine most writers do too. Want to make a character feel real? Throw in traits that you know a real person has. Take the Dude from the Big Lewboski. The Coen Brothers created the Dude as a composite character of two different people they knew, and one of them actually did have a rug that he said "really tied the room together." Classic character, that everybody loves, and knowing that he's almost a real person somehow makes him even that much more endearing.
I think the easiest way to make a character seem real is to make them like you. But I also think this is a bit of a trap. No matter how hard you try, I think most of your characters are going to have pieces of you in them, unless you're trying really hard to make them not, but I definitely think you should put forth effort to try to do it as little as possible, especially with side characters. For me it's a big turn off when every character in a book has the same voice. When they all talk the same. That's why I focus on differentiating people's speech in my books. In real life people don't have the same vocabulary list in their brains they pull from. I tend to use bigger words for certain descriptions of things, so sometimes when I'm writing a character I intentionally use a word I would never use, because it's right for the character, and it makes them sound different than the main character (who likely sounds like me, unless I'm trying to have him not. Examples of MCs I've tried to have sound different than me would be Dick from Dick and Henry or any character from my short stories). And how the character speaks tells you so much about them without you ever revealing any back story about them. You learn about a character's morals and interests as a story goes on, but you may or may not learn about their education background, their family history, etc. But by watching their behavior and speech you do get a sense for who they are, and you can infer their history, much like you would if you were people watching, or what you may do when you've met a new person and they're still a mystery to you.
So next time you're writing any kind of fiction, be sure to squirt in a little of real life in the fantasy. It's fun to write, and it makes it fun to read, by adding a sense of realism for the reader it makes it that much easier to imagine the world you're creating.