Open Group → Lists and start a list for shopping, packing or anything your folk need to do together. People who can contribute can add lines and tick them off. Shared lists are included on Free.
Claim a line to show that you are taking care of it. Only one person can claim a line at a time. Ticking an unclaimed line also claims it; unticking a line does not release the claim.
The person who claimed a line, the person who started the list, or the group owner can release it so someone else can take over. Claims and ticks do not send a notification for every change.
You can also attach a list to an event, so picnic shopping or a packing list is there when everyone opens the plan.