I voted a nappy/change bag. I purchased a really practical one and it has survived all three of my kids.
I didn't realise I could pick three so our Safe n Sound Meridian Car seat...starts as capsule then turns around to Toddler seat, another one of our baby items that has survived all three children and is still in use.
And our Cot, we purhcased a Boori cot that turns into a Toddler bed later..still going strong.

ETA: BellyBelly goes without saying I reckon