What to buy?

We went shopping the other day. Browsing, really. We are trying to figure out what we will need when Eliana comes home. Lots of people have asked us if we have registered, yet. It's hard!
It's so strange to look at stuff and try to figure out what will be appropriate for her by the time she gets home. We don't know what size she will be, how much she will weigh, or even for sure how old she will be. We are guessing she might get to come home around January or February, but that's only an estimate. She's so tiny, now, that even coming home at 8 months she might be the size of a 5 month old.
How can I know what stroller to buy, what car seat is most appropriate, or if she will already be too big for that seat or this toy?
That's when I start to feel sad. There are a lot of things that I walk right by in the store because she will be too old for them or too big for them by the time she gets home. It just reminds me of how much we are missing right now.
I'm not sobbing uncontrollably or freaking out about it. Just feeling a little sorry for ourselves.