Summary

Food is nice to have at meetups. From laid-back coffee shop chats to giant festivals, people like eating, and having something to nibble on contributes to general good cheer. Food is also straightforward to acquire if you're thinking about it, though it does have a mostly linear cost that scales with the number of attendees you have. The summary of this post is that if you run meetups I think it's worth having food around.

You have now read the basic point of this post. If you want to read on, cool, let's talk about food at meetups for more words than are strictly necessary.

Detail

You have to get the food from somewhere. 

The easiest way to have food accessible at your meetup is to host it somewhere with food available for purchase nearby and no rules against bringing food into the venue. (Some venues the rule is no outside food.) Coffee shops, mall food courts, and urban parks often work well here. The second easiest way in an urban or suburban area is to do a group food order on the spot; it's a rare civic park in the USA that can't get a pizza delivered to it, and the average pizza place can comfortably handle enough pizza to feed a hundred people on an hour or two's notice.

(My usual rule of thumb is about one pizza per four people. And yeah, pizza is my default; there are many nicer kinds of delivery food but few as universally accepted, at least in the USA.)

For more rural areas, you'll need to bring food. You can also bring the cost down by bringing food from a grocery store, very roughly by about half to a quarter of the cost. Most food is perfectly safe for a few hours, so don't worry too much about a picnic. Meat and dairy are the two main things to watch out for whether they might go bad early.

For larger events (think multiple hundreds of people) and higher class events if you want food you should expect to cater it. That generally involves speaking with a restaurant or other service some months in advance; on the low end it's still a couple of weeks. The main advantages of catering are offloading some not inconsiderable logistical overhead, usually resulting in food coming closer to on-time and having someone standing by to make sure empty trays are taken away and fresh trays are added. Such service usually costs more per person though.

Another option available is potlucks. A potluck is where each attendee is expected to bring enough food to feed their group and perhaps a bit more, and then the food is shared. This means Adam can bring an appetizer, Bella can bring an entree, Carl can bring a dessert, and each person only worries about one dish but there's a good spread of options. Potlucks in theory work at any scale, but in practice getting them to work beyond forty people requires a decent amount of social norms to be in place around not free riding and labeling things well.

Food that's easily divisible such as pizza slices, small pieces of chicken, soup in a large pot, or small vegetables works better for crowds. Most snacks are already like this, such as bags of chips or pretzels. The key word you're looking for is buffet style. Food that comes in one natural meal size such as burgers or sandwiches are trickier to predict the right portion size for, because you generate more waste and people can't mix and match as easily. 

If you run meetups mostly for some particular demographic, take a quick look at whether that demographic has any obvious and unusual food needs. Practicing Hindus generally don't eat beef, practicing Jews may keep Kosher. Effective Altruists and Rationalists have unusually high rates of veganism and vegetarianism. Teenagers will eat more volume of food than you expect; I basically count them as two people in my food arithmetic. 

More food labeling is usually good on the margin. Start with what a dish is, such as "sweet and sour chicken" or "herb bread." Allergens and dietary notes like "contains nuts" or "vegan" are also useful.

Useful things to have; paper plates, plastic knives and forks, rolls of paper towels, and a few trash bags. Given how well all of those except the paper towels pack, it's worth having way more than you think you need. If you're doing a buffet style, put the plates (paper, it'll make your life easier) before the food. The knives, forks, spoons, and napkins should be at the end though- people don't know whether they need a spoon until they're partway through the line.

Quick Tricks

Food is good, water is better. For large events my usual approach is to get a bulk box of plastic water bottles already filled; they're heavy and awkward to transport, but even given that I try to have more water than I need. People talk at meetups and that makes them want more water. Some venues will complain about you bringing food in, but very very few will complain about you bringing water. While I'm on the subject, do you know where the nearest bathrooms are at your venue?

Open the food. If you have several large bags of unopened chips or a dish of mixed fruit or other snack food on a table, people can be reticent to open them. Open the bag before the crowd arrives. Likewise take the lid off jars of sauce or salsa. If you ever want a "hot dang look at that chart" effect to test, compare how fast an open bag gets eaten compared to how long it takes the bag to get opened at a different event.

People will naturally clump around your food. This can create good lively conversation, and also for large groups it can create traffic jams. The best fix for this I've found is to have the comfortable seating be nearby but out of reach. (Ten to fifteen feet, say.) This naturally draws people off away from the food, clearing the way for others to filter in and grab something. Second best is to have multiple snack tables with different snacks on the different tables.