Best 'hack' I know of at BK is to ask for the fries with 'no salt' - that means they have to cook up a fresh batch just for you. :)
Unless you're going there right at 12:15 or so, almost every BK I've ever been in is generally slow most of the time. Airport and turnpike locations are exceptions.
source: i used to work at bk.
You can pretty much request anything as "no salt" and they will have to cook it from scratch for you. Most of the burgers and fried objects are salted when removed from the grill/fryer before being placed into the holding cabinet.
If you comb reddit you'll find previous discussions on this[1], but note that some crew members have mentioned that they premake "no salt" fries during rush periods, so you might actually be getting older fries than the ones being made continuously during that rush.
Also don't try this in the drive-thru, especially late at night, where you can't really see what's being made. Sometimes you're getting fries just re-dunked in the shortening to wash off the salt. Or worse.
[1] http://www.reddit.com/r/AskReddit/comments/s376a/my_uncle_or...
But definitely this works for the fries - when the place is slow. If it's slow, the fries have probably been sitting. If it's busy, then all those fries probably came out within the last 5 minutes, if they're not actually behind.
McDs uses heated holding cabinets that are also sealed to keep most of the product moisture in place. This was a change from the original system where burgers were fully assembled in the kitchen, wrapped, and held in an open-air heated cabinet for 10 minutes and then trashed if not served in that time.
The first time, I asked for a burger without ketchup, and it came with ketchup. I took it back, and they replaced it for free, with another burger with ketchup. That repeated again then I gave up.
The next time, I asked for a chicken wrap thing, without the dressing/sauce. It came with sauce on it, but it was like 1 am and very slow and the cashier unusually considerate, and she noticed before it got to me, and manually supervised one being made without the sauce.
The final time I ended up at McDonald's, I got a container of apple slices (with a side container of caramel which I could avoid using).
So, uh, these are just my unlucky anecdotes. Perhaps as a result, I avoid all traditional fast food whenever possible. Chipotle and other non-traditional fast food are fine.