Maybe someone could create a smart contract where the funds can only be spent at local businesses for stuff like nutritious food and temporary shelter. I think people are very cynical about giving to the homeless, right or wrong, and would be more generous if there was proof that the donations were going to a good cause and not a vice.

The blockchain would be perfect, actually. A homeless person could have their QR code on a sign, and people could send money without stopping traffic or rolling down the window. You could see what someone's balance is and their recent purchases. If someone is out there with their kids at the end of the month and then you see a transfer of a large amount as they get picked up in a nice vehicle (I've actually seen someone picked up or dropped off in nice vehicles more than once in one part of town. Parents asking for donations to send the youth sports team to Delaware for a game always work at the end of the month), you can assume they had to make their mortgage payment. I know this is cynical and there is real need out there, but even the biggest advocates for the homeless would have to admit that there is some shadiness with it in the US at least.

One solution would be for someone to create a wallet that was synched with the local community. The wallet provider would only release funds for approved uses. Once spent, the funds would be converted to the government currency and deposited in the merchant's bank. The wallet addresses would need to have a unique and recognizable descriptor that would prevent someone not in the program showing up on a corner with a QR code linked to an unauthorized wallet.