Food not Bombs
Ask around to see if your town has a Food Not Bombs chapter. FNB groups in cities across the US and several other countries serve healthy, free, vegan food to anyone who wants it. Most chapters serve at least once a week, some serve everyday. FNB groups usually serve in a public place, such as a park or town square. Food Not Bombs groups will also often agree to provide food at large gatherings, such as protest marches, picket lines, disaster areas, activist conferences, etc. provided they have the resources to do so.
Check here for more info, including an (incomplete) list of active groups.
Food Stamps (SNAP)
The Food Stamp program is always around if you qualify. Food Stamps are now debit cards that can be used like real debit cards at supermarkets for storable food goods. More information is in the 'Welfare' section of 'Free Money'.
This is a state-run federal program that gives baby formula, juice, powdered milk, and cereal to folks who have just had a baby. The food can be either picked up from a central location or bought from a store depending on the state. You can stay on it until your kid turns 5 years old. The income cut-off levels are also fairly easy to meet. 
Religious Organizations and Shelters
Often, organizations (especially religious clubs) at high schools, colleges, and community centers provide free breakfasts and snacks.
In some major cities, there are a few Krishna religious groups that often give out a free vegetarian meal if you sit in for a seminar (Fair warning: The food they serve can be VERY spicy!). Be advised the quality can vary wildly. Some groups have good resources for ingredients and skilled cooks that can make stuff that tastes great. Others are not quite as lucky and/or good.
Also, consider helping or going to your local homeless shelter. Not only can you help those in need but you can also get a free meal or two. Most shelters also have way more than they serve. Much of the excess food goes to waste. Sometimes they will give their volunteers some of the extra. Many have a walk-in cooler, freezer and pantry that are filled to the brim and at least half of it gets thrown out every week. Browse the back and take what looks good to feed you, your friends, your family and others less fortunate. After all, we could all use a free meal!
Feed a Yippie
If you are not up to direct action at least support our kids in the streets, use the large group recipes in Cheap Chow or whatever you can dumpster dive and support our troops! Please remember that we need to eat every day, put a chalk mark on the curb or sidewalk Wall Painting so we know you are willing to feed a traveling Yippie.