How to get the backpack?

You can get the backpack and more storage once you have cleared some items in the section of the board that opens up when you reach level 10. Complete one of the items in the squares adjacent to the backpack on the board to unlock it.

Backpack on the Board, unlock it by merging an adjacent item

Then with coins you can purchase more spare slots which you can use to store items safely and effectively give you more spaces for your board.

For more questions for Merge Friends check out the answers page where you can search or ask your own question.