Organizations to consider helping
St. Vincent de Paul Society - St. Vincent de Paul Societies provided resources to families and individuals in need in the local area. The link is to the national council, but almost every parish will have their own council.
Caritas Internationalis - Caritas is an international aid organization that provides assistance to local charities in disaster stricken or war torn areas.
Feed the Hungry
Feeding the hungry is possibly the easiest of the works of mercy, simply because there are so many organizations actively engaged in feeding the hungry. I guarantee that no matter where you are in this world you can find a group who is either collecting donations to feed the hungry or a group who is distributing those donations. Oftentimes these two things occur at the same location. Honestly, if you aren't helping to feed the hungry in some way, you have no practical excuse.
Volunteering to help with this work of mercy involves either collecting food and monetary donations, purchasing what is needed or distributing the food and sometimes literally feeding the hungry.