Be considerate of dietary requirements
You should aim to accommodate all dietary requirements, and be explicit about doing so.
You can anticipate some common dietary requirements in advance. Here’s a set that probably covers 90%+ of your attendees:
If you know you’ll be providing suitable food, say so upfront. Ask for dietary requirements when people buy their ticket, so you can make the right amount, or know if you’ve forgotten something.
Make sure food is clearly labelled, both by category and ingredients.
For allergies like nut- and gluten-free, it’s helpful to have details about the kitchen, if possible. For example, “This was prepared in a nut-free kitchen” vs “This wasn’t prepared in a nut-free kitchen, but separate utensils and surfaces were used”. For some people, that difference matters.
You may need to remind non-vegetarians not to eat all the vegetarian food, so the vegetarians don’t go hungry! Separate queues for different types of food, or taking people’s food orders in advance, can both help with this. Alternatively, a couple of conferences (You Got This, Open Source Bridge) have only provided vegan/vegetarian food, so there was no risk of it running out!
Note that vegan/vegetarian isn’t a catchall that magically meets all requirements – some people will have dietary requirements or allergies that mean they can’t eat the particular food you’ve supplied, even if it’s all vegan/vegetarian. (I know people who’ve been to events where there was literally nothing that was safe for them to eat.)
It’s helpful to publish a menu in advance, with a full ingredients list, so people can decide if they need to bring their own food.