A unique combination of our backstory, physical traits, emotional reactions, and relationships makes us who we are. It's the same with characters. For that reason, not all of those things have to be unique (read: OMG uber speshul) to make an original character--they just have to COMBINE in a way that makes the character compelling and able to carry the story.
The thing about backstory in particular is that experiences in our childhood have an astounding impact on us, whether we like it or not. For example, someone raised Jewish may always keep kosher even if they stop going to synagogue. Someone like me, forced to listen to symphonic music and watch Olympic ice skating even when I didn't feel like it, may find as an adult that they appreciate them and even that those things are special to them. Nothing, unless they are extremely powerful things, will ever get under our skin like the things we experience as children.
Physical traits in literature are important in a different way: they can be and often are assigned symbolic significance whether the author means for it or not. Scars are the ones that come to mind instantly. A physical scar can often stand for an emotional scar. Perfect (if extreme) example: the Phantom of the Opera. It's not just his face that's making him so messed up. Less extreme example: Frodo Baggins, scarred once by the Nazgul blade and again by the loss of his finger, could also never recover emotionally and live a normal life in the Shire.
Other things, like glasses, are simply associated with certain traits, in this case intelligence (or possibly geekdom). However, being nearsighted might also indicate a tendency to miss the forest for the trees, whereas a farsighted person might overlook things they consider minor details in favor of the bigger picture. Being left-handed has long been associated with being evil, or backward, or contrary, or just not normal. Tattoos (excluding concentration camp ones) symbolize rebellion, but the specific tattoo can also mean anything you like. Beware, however, of hidden meanings in the symbol you choose. There may be associations you're not aware of.
Colors are a big deal, too. Having a character wear a certain color can say loads about them. Also, we all "know" things about blondes, red-heads, etc. Same goes for eye color--the reason Suethors go for weird eye colors is because it's a quick and dirty way to tell us that there's something special about the character without having to show it to us with story-telling.
This might be a good excuse to get into the "show, don't tell" principle. Just because something is a physical trait doesn't mean you're showing us.
Hence the importance of emotions, actions, and relationships. It's the character's behavior and speech that really show us what they're about. It's how they handle those things hanging around from their childhood that defines them, not those things themselves. It's how they use everything they've got to solve problems, or fail to solve them, or whatever needs to happen.
And it's always important to remember that your characters can and will surprise you. It's a lot like kids: you can set them up with certain background experiences and basic traits, but eventually they will develop to the point where they start to go off in their own direction, and there's nothing you can do about it. Trying to control every detail will stifle them, leaving you with writer's block and possibly a dead story.
... I think I've talked about enough now. ^_^; I hope that helps.
~Neshomeh