My husband was definately a pack rat too. He also had the box of stuff from before we got married that he looked through maybe once a year - What's with that anyway?
I tried asking, pleading, begging, but that never works for anything so I gave up pretty quickly. I decided that we had lots of stuff to sort through, so I would "save" my husband's for last. (That was my nice way of thinking of it, after he told me not to dare to throw even 1 thing that belonged to him away.) So I started with my things, moved on to the kids things, then household (like kitchen, bathroom) stuff. By then, he had been eye witness to the bags and bags and bags of clutter that were going out the door. He honestly didn't believe until then that we had very much. Well, after all that work, I wasn't about to be responsible for the upkeep of his junk, so that became his job. Then came the real test - we moved! You never realize just how much stuff you own until you have to move every last stinking bit of it. Normally I would have packed everything myself, gotten it organized, etc. just like every other time we moved, but at the time I was 7 months pregnant with orders to rest as much as possible. So the clutter once again became his problem to pack and move. Needless to say, it's steadily been moving permanently out of our lives. He is a total simple living convert!!
So the moral of that long story
is not to worry about the stuff you can't get rid of. Start with what you can. Believe me, it will be a bigger job than you think it will and most likely will take quite some time to complete. Maybe by then, hubby will come around. If not, get some nice looking bins to keep all his junk organized.