Ooh, a puzzle.
I think I’d try to serve:
Canned soda, bottled water, coffee, tea, with packets of sugar and little shelf-stable creamers, both dairy and vegan.
The lemonade of years past!
Plain hummus (check labels to make sure there’s no capsaicin or allium) with pita and a box of gluten-free wafers.
More crackers and breads, including some clearly labeled and separated gluten-free options.
A cheese plate, with no vegetable decorations to avoid cross contamination. That provides protein and fat for everyone except the non-dairy folks, who i think can all eat the hummus. Don’t get cheese with stuff mixed in, get cheeses that are just cheese.
A separate plate with some sausages, if you have budget and space for it. I’m sure you know this, but don’t put meat on the same plate as anything you are serving to vegetarians, as it will often gross them out. The capsaicin guy will avoid this platter, so spicy stuff is okay here.
Hand fruit. That is, whole fruits people can pick up with their hands. It tends to be room-temperature stable, and with no utensils, there’s little risk it will have been contaminated. Depending on season and budget, mandarins, apples, pears, peaches, plums, bananas are all good. (Banana guy will take another fruit. He says he’s okay being in the same room with bananas.
If you can keep it cool, a bowl of salad greens, with a separate bowl of cherry tomatoes and a separate bowl of cut bell peppers, and bottled salad dressings would be nice. I’d not serve onions and garlic, even separate, in part because they can smell bad in an enclosed space. But your could throw cucumbers and radishes into the salad mix of you are feeling energetic.
Some commercially packaged candy bars / sweet snacks/ protein bars/ kind bars in wrappers, avoiding any that have peanuts as ingredients. My guess is that a candy bar made in a facility that uses peanuts that isn’t consumed by the people sensitive to peanuts will be safe enough, and they will know not to eat them.