Jealousy is a normal and natural part of human nature. That doesn't make it okay to be jealous, but even manly men have to deal with it. So how do we deal with jealousy?
It is important to ensure that you aren't getting worked up over nothing. I can't tell you whether you are really jealous or whether it is more admiration for an attribute of someone else that you would like to copy in your own life. It is good and healthy to want to be a better person - healthier, stronger, smarter, more resilient, more manly... And it is okay to admire and appreciate others who do these things better than us, so long as the aim is to learn from it.
Jealousy is a form of self-pity. You pity your own lot in life because you want something better than you have. That's why jealousy really sucks - because at the heart of it is having to admit that you are not as great as you think. Some things you can change and other things you can't. Step one in overcoming jealousy is to quit dwelling on the things that you can't change and to start working on the things that you can. So much of real manliness is in having a realistic view of yourself.
Step two is to convert your jealousy into a healthy appreciation that will motivate you to be a better person. And again, you have to be realistic in your goals here. Some things you will never achieve because you won't have the same life and natural good looks (or genetics) as the dude on the cover of Men's Health magazine.
While this doesn't directly address jealousy over material goods, the principle is the same. If you want "stuff" you have to be realistic about whether you can achieve that possession as a goal, and you have to set a plan of action to achieve that goal.
Speaking of goals, a simpler approach is to keep your focus on your achievable goals and not on the non-achievable which leads to self-pity and jealousy. Usually there is not enough time to focus on the things that you can't have anyway, but keep a look out from time to time because the green eyed monster has a tendency to creep up.