Hmmm...well early on food would have helped. As in lots of frozen meals for dinner that whomever is helping could just heat up (even if whomever is a good cook his or her services might be better in comforting a baby or getting rest for the night ahead than making food) and easy snacks/lunches for nursing mom to just eat without fixing at all. I was so hungry but it was impossible to make stuff to eat. I wasn't prepared for that so for a long time I drank a lot of boost shakes; ideally I would have had something more nutritious set up ahead of time.
And someone to help for a while while you settle in would be nice if it is possible. It would have been nice to have someone there to hold and burp a baby for example or during evening fussy times when neither could be comforted together. I was so tired and having a baby cry while I took care of his brother was so awful.
Other than that I think it depends on the babies on what is essential and what collects dust. Bouncy seats were actually really helpful here/my boys liked them best as far as slings/swings/and such went. Similarly, if babies liked slings being able to sling both would be fantastic. Or if a baby liked a swing that would be helpful. I've heard moms who loved their slings or swings as much as we loved our bouncies. (Here those other two were useless or just took up space and we moved to the garage). So a lot depends on the babies. But I do know of plenty of bouncy baby multiples. Not crunchy but in my book if a baby is happy while you take care of his twin instead of screaming it's very AP.
Baby proofing ahead of time was a great thing we did. When the boys began to roll and then crawl we wouldn't have had time to do it well.
I really loved this bathtub http://www.amazon.com/Primo-340W-PRI...0624560&sr=8-2
It's so secure and stable which makes bathing a baby while you have another waiting patiently or not so much easier. And then as they begin to sit up you can use it for both at the same time. My boys used this tub for a long, long time.
I liked onsies for warmer weather or sleepers that zipped for cold so I could change diapers easily and quickly. You don't need fancy clothes. And babies waiting while sibling gets a diaper change often weren't happy around here so doing it as fast as possible was important. And have a good diapering station or two set up and ready to go.
Oh! I almost forgot. My number one best item were miracle blankets for swaddling. Must have here; definitely helped in so many ways sleep and comfort wise for my boys. White noise was nice too.