I used to think this was extreme as well, but now know that it's a necessity (for me, maybe not for other people) to pack well in advance (can I claim to be more obsessive compulsive than you if I admit that I packed over a month in advance for my last trip?)
I also have a regular checklist I made up a long time ago of basic things that are divided into categories ("Clothes," "Toiletries," "Entertainment," "Documents," etc.) so I'm less likely to forget anything.
The past few trips I've made, I not only had to pack far in advance, but also write down some specifics of what I packed ("red ninja t-shirt") because otherwise I'll forget if I included something to wear to church or not, etc. I'm also a chronic over-packer, so packing in advance gives me time to see what I use in my current normal routine and hopefully swap a few things out.
While I'd like to tell myself I'm just "being organized", perhaps "going stupid crazy" would be a more accurate description.