How can a researcher improve his contribution to society? As an academic researcher in a theoretical field at a public institution, I am sensitive to the social value of my work (my own contribution to society). I do some teaching, whose contribution to society is easy to identify, but not much. Try to increase that aspect of my job, I have listed some things I can do (some of which I already do, some of which I don’t):


Engage in collaborations with industrial partners (favoring transfer of knowledge to practical applications).
Orientate one’s research goals to match an area of societal importance (green gas reduction, nuclear waste storage, you name it).
Communicate science to a wide public, whether it is my own research or the knowledge of my field in general (popular science). This includes writing articles in magazines, writing a blog, developing educational software, … 
Get involved in education science: contribute to my national society of physics and chemistry teachers, for example. Offer some software for high-school and university teachers to demonstrate concepts.
Register as an expert with the nearest court of law.


What other suggestions do you have to improve one’s social value? (Or should I stop worrying and love the bomb?) I mean, in the short term. I know that I (and my colleagues) contribute to the advancement of mankind in the very long term, but sometimes it doesn't help feel useful.
On a different note from some of the other answers, try to take to heart that basic research is directly useful to society. Almost all modern pharmacology is based on decades of fundamental biochemistry and biology research. Materials science is based on years of basic chemistry and physics research. Basic math research fuels advances in all types of engineering, from signal processing to computational work to structural engineering. There are many other examples for other fields of research; please edit this answer or put them in the comments. 

In short, don't underestimate your current value to society.