I know most of the organizers for tech meetups in my area. They all tend to handle the case of food differently
- One takes donations through patreon, which has worked fairly well. They have an actual board of directors, so it's very legit. I'm not sure if other cities have anything remotely close to this though.
- For popular technology meetups (react, .NET, etc), usually a recruiting firm will sponsor the pizza. They contact the organizer generally. Usually they will do a 2 minute blurb at the start of the meeting
- For meetups that are part of a larger organization, they tend to get funds straight from corporate. E.g. CodeForAmerica, GoogleDeveloperGroups, etc.
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As a side note, I kind of wish it wasn't only just pizza. Some healthier options would nice. Some meetups use jimmyjohns or chickfil-a instead, which are nice alternatives.