Dana, your best bet is to wish for items at different price points and to also include items that can be easily divided, like dimensionals. Those sorts of items come in handy when I am trying to even out the value of the bags. The 5th stamp case that Arlene mentioned is another good example of a shared item.
I would go for some things you might not otherwise consider buying. We could talk at Saturday's stamp-a-stack. I sure have plenty of ideas!