In Resources, you can use the "Zero Price" tick box to mark items that you don't charge for.
By doing that, you'll reduce the risk of accidentally charging for complimentary items.
They will also show up a little differently on the Planns screen, with nothing showing in the Payment Method or Balance columns.
And you won't need to add the payment method to make them disappear from the Planns screen at the end of the activity day. They'll do that automatically.