the merit in any act of charity lies in whether or not it is done for love of Christ, as described in Matthews gospel, when you did it for one of the least of these, you did it for Me. The purpose of traditional penitential acts, fasting, alms giving and prayer, is first of all conversion of heart so that we become ever more closely united with Christ, leading to the virtues of humility and obedience. The extent to which any charitable works is a source of grace lies in the extent to which we identify the recipient(s) of the act with Christ.
If working in a soup kitchen leads us to be able to see Christ in those whom we serve (especially the most un-Christlike) that is a source of grace. If it leads us to condemn them for their condition, that is an evil.
There are 7 spiritual and 7 corporal works of mercy, not all of us are called, as St. Paul reminds us, to do all of them all the time. Most of us are called to one or two of them most of the time, and the rest on occassion.