Great question!! They are simple, but not intuitive. Select your desired pledge level, then change your pledge amount to include any and all add on that you want. For example, you want EVERYTHING!
Select Greenhorn Tier - $49 then change your pledge to $63 ($49 + $7 meeples +$5 mini-expansion + $2 Salvage Yard)
At the end of the campaign, the survey will give you the opportunity to verify the add-ons plus the crack staff at Gryphon Games will have a good idea what you wanted based on your pledge amount.