Regardless of quantity and tracking, you can still choose to show or hide a 'Quantity Available' - even if it has nothing to do with reality!
For instance below you want an 'unlimited item' like a raffle ticket.
>Select or Create the Item in Registration Items
>Make the Quantity 1
>Do not check Track Quantity
>Check Hide Quantity
On the front of the website you will end up with an item that is NOT showing any quantity, and will NEVER sell out - until you manually make the quantity 0.