You can use Marketing Lists, create one for 'Gift Voucher' and add the 50 contacts. You can do the same for your other lists.
If thats not a good option, you can create some sort of N to N or Contact to Many - 'Event Storage' type table. Create a record tying the Contact to that entity, one record for each 'list' they are a part of, then you can track it that way too.