I never used the traps or poisons in Dragon Age Origins, but then again I barely used enchantments either from both DAO and DA2. I don't know why, I just didn't feel the need for them, combat was easy enough anyway.
I never played Blitzball in Final Fantasy X. I didn't like it, to be honest I found it more slow paced than anything and it was a game of numbers. Would have been great if it was like a football game and played like it, but eh, it doesn't really matter much.
The Seed Maker in Harvest Moon A Wonderful Life. Partly because the scene where you unlock it for free never really happened for me for some reason. I will try and figure it out in this play through. But also animals were always the main focus of my farm, so I didn't feel the need for all those seeds.
I don't know if it counts but when I first played Kingdom Hearts 2 I finished it without leveling up anything, without changing keyblade, without getting any skills or abilities. I got to the very last boss when I realised I had all that stuff. I felt like an idiot but at the same time proud that I got that far and finished it without that stuff. Never done it again though, combat is much better with an updated keyblade.