A while back, I was tasked with writing an article for LP national about various members of the movement doing good works. You know... helping out the disadvantaged apart or adjacent from politics and absent government. These were people doing primarily local efforts that avoided red tape and huge NGOs that spend so much of their donation money on advertising and unnecessary overhead. Some of these efforts were technically against the law... feeding the homeless without a food handler's license, or bringing tents to them in communities the government was trying to fence off, etc.
Our local chapter had just called it homeless outreach. The Cajun Navy people had some colorful terms in endearing accents. Some of the more doctrinaire libertarians called it a part of "voluntaryism", a tradition harkening all the way back to the Levellers. When I talked to the Liberty Memes guys about what they do with wheelchair vans and the like with their five dollar organization, they called it "private charity" and put their emphasis on the private bits. When I talked to Vermin about his VSI organization, he was really keen on the phrasing "mutual aid", wanting to follow in the steps of Kropotkin and all that entails.
But I was just listening to Rob McQueen of Waves for Water, and he used the phrase "guerrilla humanitarianism". In terms of marketing, it just sounds much more badass than any of those other options. I'm totally pirating his phrase every chance I get.