Not from a martial arts point of view. 
More arms. I’d love to have three per side.
The human mouth and anus need to switch positions. Eating nonchalantly while sitting on food has innumerable sociological advantages. Of course we’d have to learn to talk out of our asses to complete the scenario.
Some would argue many have mastered *that *trait already.
Reroute the urethra so that it does not travel through the prostate.
Completely separate the digestive tract from the respiratory tract so that we could talk and still do oral things at the same time (eat as an example)
Eliminate all body hair except brows, eyelashes and head hair.
Reroute the reproductive system so that it doesn’t center between the legs. Maybe up about half way to the navel. This would allow easier birthing as offspring wouldn’t exit through the floor of the bony pelvis and sexual activity would be less prone to infection. And dancing close could be really fun!
Extend the spectral sensitivity of the eyes so that we could see how hot objects were, and get more information in the ultraviolet end of the spectrum like some insects, birds and other mammals do. Make our eyes cataract proof.
Give us third eyelids that protect the eye and give the correct refraction in water so we could see underwater.
Make our teeth with additional replacement sets that give us new teeth every decade or so.
Eliminate acne.
There are so many great ideas in this thread that I will have a hard time going to sleep.
I am already mixing & matching some of them.
Multiple orgasms for men.
This! Teeth are a huge nuisance to maintain.
I asked my wife about it and she said inflatable boobs. Double D’s when you want 'em and A’s when you don’t.
The serious answer would be better brain circuitry so that mental disorders wouldn’t happen.
Let us lay eggs. Small eggs, that take months to incubate outside of the body.
Also, as people mentioned before, constantly growing teeth and better joints. (Esp. fingers/wrists. Damn ye, carpal tunnel.)
Retractable sexual characteristics would be pretty useful in general. Be taken seriously in situations where gender should be irrelevant, stop guys hitting on you at inappropriate times, but a night out on the town? Boobs out, arse out, waist in!
Creepy guy staring at you? In they go! Hot guy glances over? Out they come!
Control of ovulation would also be pretty damn helpful.
Yeah, complete control over ovulation would be good, as well as the ability to consciously terminate a pregnancy in its early stages.
Adjustable boobs is great too. Get pulled over by the cops? Whump, double D. Need to run a marathon? Whump, A.
I would like the ability to grow a thick, luxurious 'stache and beard. The 18-foot black hair growing from my middle-age lady chin doesn’t count.
And the option to not have boobs at all!
Better knee and spine design to eliminate common problems.
Women have the ability to consciously control their reproductive system, and only get pregnant when they choose.
Make women as large and strong, on average, as men. Alternately, get rid of dual gender biology and make everyone hermaphroditic – everyone can get pregnant (with the ability to control it), and everyone can impregnate someone else.
Armour plating on top of skull, temples and back of neck extending down to mid-shoulders.
Four pairs of eyes like spiders, with indirect eyes lined with tapatum also like a spider’s.
Electroreception, like a shark, so as to better know when your kids are texting as opposed to doing homework.
Cartalaginous skeleton.
Big bushy squirrel tail to maintain balance while on bikes and make it a nice colour to better attract the ladies.
I’m surprised there isn’t more enthusiasm for ‘boobs on the back’.
Yes, and I’ll take a throat vagina / throat penis with them.
Esophagus nowhere close to the trachea.
Perfect vision in all light (or dark) conditions; ability to morph into microscopic and telescopic vision at will.
And why is this 
wearing sunglasses, anyway?