Occlumency

No, Harry doesn't have remedial potions (despite what you've heard). He is being taught the art of occlumency, the blocking of one's own mind from external forces. Professor Snape has reluctantly accepted this task, and so far Harry's not doing so well. I don't think I've ever seen so many diverse bottles and vessels together in such a small space as in this MOC by Vaionaut. Snape certainly keeps his shelves well stocked.