Tell them about how they can unionize and safely organize their coworkers without getting fired. Give them contact info for the IWW, especially through any drive through service as multiple workers can hear your spiel at the same time. Don't let them respond because you don't want their manager to think they're asking you questions but announce to every worker you come across that they should unionize and even write it down on the receipts. People don't know their options, they don't know that others support them, any news or social media outlet won't give them the complete picture, if you're the consumer, you have a direct impact on their behavior at work and might be able to share something with them they need.