I believe it would be the interaction with kids and propagating the dream of a developed India. Having some one for the young generation to look up to, in my estimation, is very important. He would have been such a figure even if he was not the President, but, by being a president he had more previleges that he put to this use.
BTW, what was the greatest achievement of any president in the modern era, say, from the 1970s or so? Do you expect the president to indulge in policy development, decision making, or any of the other functions that come under the PM and the council of ministers or the parliament???
And if Kalam was the PM rather than the president, he would definitely have worked towards all of the stuff mentioned above.
