Typical soup kitchen volunteering is pretty low impact. It's the first thing a lot of people think about when it comes to volunteering, and people like that they get to interact with the less fortunate. So they show up with their church group a few times, ladle some soup and that's about it. Running a soup kitchen is different and higher impact.
The things the UN is doing matter to millions of people. If you work with the UN food program, you're dealing with food by the truck load instead of by the spoonful.