I have a question. Most drinks have a best by date on them. How long do drinks actually last though? I have drinks that are out of date in cans and some are way out of date. Will they be bad to drink? I tried some that were a couple years out of date and they seemed fine. What is your experience with out of date product in cans.

Cans or glass with sugar (or HFCS) have always seemed to keep well for 2+ years in my cellar. I've had a harder time with plastic bottles. They might keep their fizz and flavor for a year if I keep them chilled in my extra refrigerator. They are pretty much spent after 6 months if keep them at room temperature.

Plastic bottles don't last long for me either.

I think its all really predicated on the way the product is stored. I had a few cases of Diet Dr Pepper in my basement that was one year out of code. I tried one just to see what it tasted like. It tasted fresh. However, it was about a year round temp in the mid 60's with no sunlight in the are where they were stored.
For the record....I drank all of them with no ill effects.
On the flip side, I've had regular Dr Pepper that was stored in my garage where temps fluctuated as well as the sunlight and it was in code and tasted flat.

Generally artificial sweeteners tend to break down more quickly that sugar of HFCS. But the most important thing is a cool place to store em. As the old rotation saying goes: keep it dark, keep it cool, keep it moving. Plastic's not much good for long-term storing.

I keep my soda pop in a cool dark part of my kitchen.
I take great care to keep the 2 lts standing straight up.
A cool floor is the best way to keep soda pop fresh other
than the fridge. Dark and cool will keep your soda pop
oh so tasty.

As stated, keep them cool, and they last longer. The lifespan shortens drastically in heat. Plus you want to keep your drinks out of direct sunlight.

Cans and glass bottles should do very well. Plastic is air permeable, so I would imagine it's lifespan is much shorter. It might retain most of the flavor, but lose carbonation.

Once I was really thirsty. I was at someone's house and found some (And this was 2007) 2002-2004 Diet Pepsi/Dr.Pepper. Unfortunitly, my brother got the Dr.Pepper, and I didn't really know how bad diet soda tastes after the experation date. I tasted some of the Dr. Pepper poured into a glass. I guess it was about Cheerwine with a bad aftertaste. Now the Diet Pepsi I got, well...
It smelled fine. I got my hopes up, but I couldn't get the stuff down my throat. I believe that might have been my first "diet" beverage so I was horrified by the taste. Well, sometimes its just better to dump the soda and collect the can!

Do all diet drinks have the same shelf life? I know that Splenda is chemically more stable than aspartame is. Do Splenda-sweetened drinks have a longer shelf life than those sweetened with aspartame or aspartame and acesulfame-K?

There are a lot of variables in this scenario.

1. What type of sweetener is used?
* HFCS lasts longer then pure sugar. HFCS two plus years. Sugar one plus years if stored properly
* Artificial sweeteners like aspartame have a short 4 to 8 weeks

2. Filling process
* Hot fill or cold fill

3. Package
* Metal package is preferred for longer lasting shelf life. They contain the CO2 molecule better and block light
* The CO2 molecules will permeate the plastic bottle causing the product to go flat within a few months

4. Chemistry of the product and the reaction of the ingredients within.

5. Quality of the water used in the finished product.

6. Storage, refrigerated or room temp.

There are a few others but these remain the top 6.