You can purchase all unowned items that are still available for purchase in-store shown in the Top Look carousel image when tapping on the "Buy Look" button, in the following order:
Hair accessory
Prop pack

In the case where you are low on diamonds, you will be directed to an "out of diamonds" popup to purchase some diamonds first.
You'll then return to the buy look popup to finish the transaction!

Note: If you do not own a hair accessory credit or prop tokens prior to tapping "Buy Look", you will be directed to the premium store first. Once you have successfully obtained a HA credit or Prop tokens, you can then unlock the hair accessory/Prop pack.