It is possible to add something called a “subtask” to both tasks and events. This can be used as a shopping list, listing milk, sugar, potatoes on a task to do shopping or in the use case of Event (barbecue), “Bring beer”, “Bring meat” etc will be possible for all attendees to assign to themselves by either completing them immediately by simply checking the checkbox next to the item.

First you have a list of items

Once you check off an item, it will be moved to “completed / accepted”

This will also work if there are several people on the same task, for instance, if someone else buys Eggs, and checks this box, it will be automatically moved to the “completed” section with the name of who completed it.