If the gifts are packs then you will get up to 7 items per pack and each item is a random roll. We have to have enough inventory space for 7 backpack items, 7 TC, 7 of any reagent, 7 jewels (might not apply to packs that don't drop jewels). You can move these to the shared bank or put the TC into a deck to free up enough space.
They prevent you from opening a pack if you don't have enough space available for any possible combo of drops to make sure you don't lose anything you've bought (or been gifted).
