Those are the best items in the game, by far. You get the seed or fertilizer (I forget which is which too) from the Shy Away when you beat the Megasmilax (who incidentally is a hundred times better than Petey Piranha), and then the other after you beat Valentina. That's when you use the walkway.
Yeah, the Lazy Shell weapon is the best in the game, and the armor is also the best. Whoever you have the armor on will basically lose 1 HP, no matter what attack hits them, except for big bosses (Smithy, Axem Rangers, etc.).