Abdullah ibn Haarith (may Allah be pleased with him) said, “I did not see anyone who smiled more than the Messenger of Allah (pbuh).”
Smiling is the easiest charity we can give. It's a strange idea to wrap our heads around sometimes, because we often think that charity can only be given by those with a surplus of wealth. And Lord knows that as university students we are generally not among that group. But it takes a kind and generous heart to smile and maintain a pleasant demeanor. By smiling, you are giving a piece of your good character away for the benefit of others happiness. Subhanallah, even under financial burden, we are still given the opportunity to give charity.
Why so serious? Smile, it's sunnah :)