What to do with stock parts?
 

What did you guys do with your:
Stock wheels
Stock exhaust (cat-back)
Stock headers

I can't hold them anymore, it's all taking up too much room and I don't see myself going back to any of it later.

Is any of it valuable?

I store them until it's time to trade the car in and then I either put them back on the car or if I'm selling the I include them with the car when I sell it and usually can get some extra money when it comes time to sell the vehicle.

However more often then not I trade the car in and revert it to stock before doing so unless the dealer will take into consideration the work done to it sometimes they do sometimes the don't if they don't they get a stock car if they do they get a modified car and I then ebay the stock parts.

Wheels, if you're willing to ship them, can be sold quickly here on the classifieds. I've had no luck selling mine on Phoenix Craigslist, though.
I'd always keep the exhaust in case you sell or trade in your car.

Sell it and then re buy later when you need it again if you can't store them.

I sold my stock wheels/tires/TPMS a couple weeks after getting the car for $750. They lasted 2 hours on Craigslist.
Stock exhaust and headers will likely prove to be more difficult to make money from.