Am I allowed to Buy Seeds, Blocks from the Gem Store? And If I am Allowed to, What Items are not Allowed?

I'm not a mod but this is what I would say.

It shouldn't be allowed because of RNG. If you buy a seed pack and get a good pack. It would be extremely unfair for other runners.

For the splice category, only seed packs are banned, but the use of growspray purchased with gems gained during the run is encouraged. I don’t believe any other category would have any use for shop purchases, but there aren’t currently any restrictions for it