Donating money is almost always more valuable than donating time, especially if you're not going to donate a lot of time. The time may feel better (or it may not -- I've had volunteer gigs where I didn't feel I could accomplish much, and that sucks), but the money is more useful.
The economic consideration comes down to the real value of the labor, and that depends heavily on the economic benefits of specialization. A day of you doling out soup to people or picking up trash won't be worth any more than what someone who does it for a living is paid. And it will probably be substantially less because you're not practiced at it. A day of you building houses (assuming you have no training) could…
Is it?
[We] seem incapable of stating the obvious truth: that we who are well off should be willing to share more of what we have with poor people not for the poor people's sake but for our own; i.e., we should share what we have in order to become less narrow and frightened and lonely and self-centered people David Foster Wallace