2008 E91 acquired Nov 6, 2012. First Mod was the "Seat Crap Delete" Mod. That's the one where you pay someone for 4 hours work to scrape 4 years of all manner of Crap from between the Seats, and everywhere else.
Second was to remove the 35% / 95% (?) tint and replace with 23% all around. The front tint was so light the installer quoted me wrong - we didn't know there was tint on the front until they went to install the new one.
Next was the "Canadian November Mod" where we remove all the rubber from the rims and apply softer, bumpier rubber in the form of winter tires from Tire Rack (bought 12 winter tires this year... ouch).
Then the "Greasy Start Button" fix. Marius76 shipped me a lovely replacement button from Poland and I replaced it - looks brand new again. Not a Mod, but a fix for what is arguably a design flaw.
I have been waiting 1mo and 4 days for a stupid DCAN cable being drop-shipped from god-knows-where (I ordered it before I even picked up the car). That will lead to a number of coding mods.
I have been waiting exactly 1 month today for a handful of 2500K bulbs from <company name deleted to protect e90Post, but rhymes with schmee schinety schmoo schmighting...>
to replace all my primary lighting (HID stays...). I ordered THOSE before I got the car also... still waiting. Won't likely buy from them again, if I EVER even get the bulbs at all. I have received a half dozen orders for things from around the globe (Marius76's package from Poland arrived faster...) Still waiting for these from the USA. Go figure.
Debating black grills, but I think I like the chrome-on-Monaco.
Spring will bring new wheels.
Future mod list, like the OP, will last me the life of the car...