Fear not! Once you've made an in-app purchase, you will always be able to redownload it again for free. It's a buy once own forever type deal.
Just make sure you're logged in with the same iTunes account you initially purchased the pack(s) with and goto download again.
You will be prompted to purchase the pack again - press OK and the app will tell you that you have already purchased this pack before and will ask if you want to download it again for free. Press yes and you're away.