Contribute more ideas in comments and I'll add them to this post!

Ideas crowdsourced from UK Organisers, Eindhoven Syllabi and this^[1]. Consider that universities have rules on individually packaging items, to avoid contamination. I'd strongly suggest having some options for those with Coeliac and allergies, if not everything is individually packaged. 
 

The List (roughly ranked according to me):

• Whatever snacks are in the grocery store aisles, especially slightly fancier stores- Oreos, Apple Pies, Jammy Dodgers are vegan
• Cookies - Grocery stores, Insomnia, Ben's, Crumbl Cookies. Whatever's close by
• Doughnuts - Same as above
• Party Rings
• Starbursts
• Rubicon, Fizzy drinks (in cans for the environment and stack-ability)
• Homemade Bubble Tea
• Protein Bars - Trek Bars are good in my opinion, , watch out for honey in e.g. Nature's Valley
• Grapes and other Fruits
• Nuts (Watch out for Allergies if they're not individually packed)
  
   

1. ^{^}

   In case the link dies, it's a tabling guide which also says: 
   Have a low bar for handing these out, not a big deal if someone has one and doesn’t stay for a pitch.
   Remember to make sure the food/brands are visible from a distance