You hand each guest a sealed envelope at the beginning of the show. You can leave them unsealed but use resusable stickers to seal them so you dont have to keep using new envelopes with each show. Instruct the guests not to open the envelopes until you say to.
At the end of the show, either before or after the guests place their order, you remind everyone about their Special Gifts for You envelope. You then tell them they are only allowed to open them if they book a show with you!
If you have one of the gifts is far superior to all the others, you can build it up by saying And in one of the envelopes, there is _____. But you will only find out if you have it if you book a party! If you are concerned that the first person to open might have that superior gift, you can get everyone to book first, then everyone that books gets to open their envelopes together.
This game is effective for getting new hostesses, because most people are so curious and want to know what is inside.