Everything except for life, that is. I wouldn't say it takes a Harvard Medical School education to come to this realization, but I am going to let you in on the secrets hidden in the confines of a $400,000 degree:
I've known rich people who feel inferior to friends who are even richer. The key is spending less than we earn, growing other values, and just ignoring (or laughing at) all the blandishments of an economic system dependent on our cravings every last thing we can get.
What stops us from having the very things we say we want in our lives is usually ourselves. Whether it's feeling that we don't deserve those things or that we don't believe it's possible to get them, it comes down to changing our thinking around it.
Yes, we all need a roof over our head and food to eat. We all need love and some form of a relationship we can rely on. We all need the basics to sustain life, but YOUR happiness doesn't lie in attaining those basic needs. It lies in the details of who you are as a person.
Although I often find scientific means of measuring happiness analogous to trying to measure milk with a ruler, it is clear from the research of scholars such as Martin Seligman and Ed Diener that there are definitely factors and choices that contribute to overall happiness.
My experience is that too many of us under-value, or fail to recognize, our true worth. We do not take good enough care of ourselves, or we sell ourselves short when it comes to being true to ourselves and going for what we really want in our heart of hearts.
Instead of panicking about a state you have not yet achieved, I urge you to live in the magic of the moment. Do not let thoughts about where you could have been, should have been, or need to be dominate your psyche.
In the end, it doesn't matter how much one has. If you live in an inner conversation of scarcity and lack of awareness about and acceptance of who you are, you are not much better off than a homeless person.