I'm considering having twins. What do I need before I start?

I will forgo the obvious things, like "two car seats." If you didn't already know that, you shouldn't be breeding in the first place.

• A sink-side instant hot water dispenser. There was one in our house when we moved in -- pretty much the only modern amenity. It was deemed useless for the first six years, but wow, has it paid dividends.  There is no better way to warm a bottle.
• Tivo. I can't stress this enough, especially if you decide to have your twins after having another child.  Actually, I recommend this even if you don't have twins.  And I know a lot of what there is to know about watching TV.
• Two bouncers, preferably with vibration technology.
• A co-sleeper for the side of the bed.
• A minivan, preferably one with remote-controlled motorized side doors.  You do have to give up a little bit of your self-respect when you drive a minivan, but the convenience you purchase with that missing self-respect makes it all worthwhile.
• A third adult in your household.  We made the mistake of undertaking this without securing this item, and now we've lost all negotiating leverage with potential bigamy prospects.  Live and learn.