I was sick last week, and 2 weeks before I had the government medical exam. Both of these got me to thinking about physical issues. We all have them. Here are some that you can use with your characters.
If you're writing YA like me, or Women's/Chick Lit (as I hope to some day), then body issues can be a big deal. For females, breast size and butt size are probably the biggest issues. I see breast size issues a fair deal in YA. For guys, I'm not sure what the biggest physical issue would be. I imagine that it's anything that makes a guy feel "uncool" - gangly limbs, stick-y out-y ears, etc. Remember, people can get obsessed about the weirdest things too. We all know people who freak about something we consider tiny.
Here are a few issues, you might give your characters:
Breast size - like I said, a common issue.
Butt size - especially among Blacks and Latinos, who like a big butt, and among Asians, who may like a small one.
Other sizes - noses, mouths, eyes, ears, hands, fingers, toes, etc - too big, too small, too long, my thighs are too big
Shapes - a body part that is shaped funny, like my little toenails stick straight up in the air
Unevenness - one foot/breast/ear/eye/etc is bigger/longer than the other
When you've decided on your character's insecurity, be sure to follow all the threads. For example, my thighs are to big, so I hardly wear shorts. Now, if you're writing a character who hates her thighs, you don't need to say she doesn't wear shorts, but you probably won't write a whole bunch of scenes parading her around in Daisy Dukes.
Also, be sure to sprinkle in the insecurities. You don't want your character to sound to whiny. And if you have a lot f characters with a lot of far-fetched issues, it may seem contrived.
In addition to body issues, there are also issues which are purely physical. For example I have bad veins, so anything involving needles takes an inordinate amount of time, and I end up like a pin cushion.
Obviously, there are huge physical issues you can inflict upon your characters- disabilies, diseases, etc. But there are smaller problems that people face. Here are a few physical issues that your characters might have to deal with:
Heightened/lowered sense of sight/hearing/taste/smell/touch
Sensitivity to... -I'm sensitive to electricity. When we did the medical exam EKG, I could feel the current. I get shocked by walls and doors in winter. People can be sensitive to all sorts of things.
Various aches and pains
Proneness to colds/ gastro/ throat infections
Some physical issues will affect a character every day - like colour blindness, others -like my bad veins- only matter in a specific set of circumstances.
The physical is a huge part of your character. Make sure that you don't overlook or underpaint it when building characters.