I found this great twin baby registry list. I posted it on a thread. Hope it helps!
I would agree with most of that, the only thing I would say is I could not live without 2 bouncers because I feed them both in them at the same time and they love to play in them too (buy ones that you can remove the toys thing as and when you want to feed them)
We've always got a swing but never really used it, I wouldn't rate it. And we got bought 2 of those rubber ring things to help them sit up, and we only use one very occasionally. We used it in the beginning when they were tiny because we used to lay them both on it (we put a cushion in the hole in the middle and a blanket over the top).
We only have one monitor and that easily picks up both babies, we just put it on a little table between the cots.
I would def recommend 2 bumbo's ours are just big enough to sit in them and they love to sit opposite each other and look at each other.
Def only one mat needed, our one is more than big enough for them both and they like to play together - feel and grab each other
We bought 2 of those bath seats (like mini bouncers) and we've not really used them, its easier to hold them and let them splash and float about in the water I think, but thats just me, other twin mums couldnt live without them.
We had 2 moses baskets and now they are in their cotbeds so def need 2 of those, I do put them in together for afternoon naps sometimes though, bit of twin bonding time (I am selling my moses baskets if anyone is interested! Mamas & Papas practically brand new with stands PM me)
Thats all I can think of for now! I would say try not to buy too much before you know if you'll need it, see what you think you would use as you go along