Can anyone recommend any songs?

So here�s the deal, I am finishing at my current school in summer, and when we finish the headmaster wants me to perform a song on stage!! But however that�s not the problem, the problem is, I haven�t got a clue what song to sing and play (guitar). He wanted it to relate to our ending of school but that doesn't help me at all. I would be very thankful if anybody could recommend any good not to hard to play/sing songs that could be good. Thanks!!