pixel_player72254710 you can't have it in your backpack until you can buy it. Here the "purchase price" that you need are the ticket and the slots.
What do you need specifically to dig out the two slots? Focus on getting those items from every source possible. Do the appropriate repeatables. Send caravans to get those materials. Check for other repeatables such as Cache that also provide stone and lumber. If you have 100 gems then look at the Wiki to see which of the older events would be worth doing for the stone and or lumber they yield.