Remembrance for at a gathering (like a meeting):

Rabb ighfir lee watub ^alai, innaka anta attawabul ghafur.
O Lord forgive me and turn towards me, verily You are the Oft-Returning, Oft-Forgiving.

Supplication for when ending or leaving a gathering:

Subhanaka wa bihamdik, la ilaha illa ant, wa astaghfiruka wa atubu alaik.
Glory to you (O God) and Praise be to You, there is no God but you, I seek your forgiveness and I turn to you (in repentence).

Supplication for one who's affairs have become difficult (like too much homework):

Allahumma la sahla illa ma ja^altau sahlan, wa anta taj^alul hazana itha shi'ta sahlan.
O God, there is no ease except in that which You have made easy, and you make the difficulty, if You wish, easy.

You may also wish to see the complete list of supplications from the Hisn Al-Muslim.