It
is important to remember the needy all year-round. On Purim, especially, it is a
special mitzvah to remember the poor. We should give charity to at least two,
but preferably more, needy individuals. The mitzvah is best fulfilled by giving
directly to the poor. If, however, you cannot find poor people, you should place
at least several coins into 'Tzedaka' (charity) boxes. Even small children
should fulfill this mitzvah. What kind of gifts should you give? Give at least
two kinds of foods which are ready to eat. 
Adapted from http://www.bus.ualberta.ca/yreshef/purim/mitzvot.html