I always suspected that one of the best ways to carry enough oxygen for a long trip like the one to Mars would be having plant life aboard. This website however, claims that you would need a ridiculous amount of plant life in order to generate enough oxygen for one person (note the very professional use of Comic Sans):
http://www.astronomycafe.net/qadir/q767.html
So cut the plant life aspect out of the plans and you're still stuck with the reality of having to recycle urine [http://www.smartplanet.com/blog/science-scope/how-nasa-is-recycling-urine-into-drinking-water/6246], or more likely,
other people's urine and probably have to drink it. Bottoms up!
And God forbid you actually require surgery en route to Mars. They're working on that [http://www.usatoday.com/story/tech/2012/10/05/zero-gravity-surgery-device/1614615/] as well.
Then you have the likely terror of solar flares and having to flee into a space age panic room to protect yourself from the high energy particles.
Ah, screw it. If they'll take me I'd go. At the very least just to see the effects of time dilation [http://en.wikipedia.org/wiki/Time_dilation] from the trip.