Cold lunch ideas for a large group?

You could make some sort of pasta salad. I've made an Italian antipasto salad with pasta, diced pepperoni, black olives, diced mozzarella, diced artichoke hearts, thin pieces of red onion... pretty much whatever you feel like throwing in, all tossed in wishbone Italian dressing.

I've also made a taco pasta salad: ground beef with taco seasoning, cheddar cheese, black olives, green onions, with or without tomatoes, all tossed in Western dressing.

They all taste better if they've had a chance to sit overnight, but that can dry out the pasta a little, so when I take them to potlucks, I usually take what's left of the dressing. (Here, I'd probably bring an extra full bottle.)

Fruit would be a good side for any pasta salad, and I'd stick with some simple cookies or brownies for dessert.

sandwich, fruit, brownie. chips and bottled water

I’d make something that can be kept for a few days without refrigeration in case the people only eat half and save for later. Fruit, either whole or prepackaged fruit cups; nothing with mayonnaise or anything that could go bad quickly; things that would pack well and not get easily crushed or bruised (so maybe not fruit but the fruit cups); bottles of water.

I work with our church to provide "to go" sack lunches for the homeless shelter a couple times a month. We've learned a few things through the years, namely to keep it simple. These people are on the go so they want things like sandwiches that they can carry with them (often stretching a sandwich to more than one meal) and they often times have bad dentition so things need to be on the soft side. Even a good bread with seeds is sometimes hard to eat. Also, when given a choice, they will probably want a soft fruit like a banana, a fruit cup or a jello, rather than a whole apple... again because of problems with their teeth.

Stomach issues are another problem so avoid spicy anything.

We've had a good response to peanut butter/jelly and cheese sandwiches. Also individually wrapped breakfast bars, soft ones like Nutri-Grain and cookies (served in baggies so that they can be saved for later) are appreciated.

Make a simple lunch of pasta salad and cut up fruit and water with a to go bag of snack foods: granola bars, fruits, water, etc.

I volunteer with an out reach program and we do

ham and cheese;
roast beef and cheese;
just cheese; and
pbj.
all on white bread

IME the pbj and ham and cheese are the most popular

We also sometimes (depending on donations) do
salami wrapped around a cheese stick

For sides we do bananas, grapes fruit cups, granola bars/cookies and chips

The people we serve would not be interested at all in frittata, or pasta salad or antipasto, although they sound great to me.  They want quick and easy and filling

Ds was helping a friend that was doing this. When he was little I would make him a pbj club sandwich with 3 slices of bread for field trips. He suggested they do that when helping at his friend's. They were a huge hit. They still fit in the sandwich bag and offered ample for later.