What I know for certain:
168 item script Message
"String" is now available as an option on the Pickup tab of an item's properties, and even allows you to choose whether you want the string to display every time you get that item or only the first time you get it. You can also have the string only display if the item is held up (set under the Screen Data menu as before).
Heart Container Pieces don't allow for incremental messages per piece though, so you'd have to keep that script.
324 ffc script LockedDungeonEntrance
Lock block combo types can now be set to use any item (and any amount of that item) to unlock them. Set the type to "Lock Block (Normal)" and go to the Attributes tabs to see the options (including Sound Effect and Eat Item). The only thing I see this script has that the engine doesn't have is the string that gets displayed when you don't have the required item (could be a nice feature request for the engine though).
Other things may be possible to varying degrees, and it's highly likely that some of that code could be further optimized to more efficiently use 2.55's expanded scripting capabilities, but other people would have to advise further.
