Basic Save/Load

[arces]

Loading and saving progress in some kind of file format. JSON? XML? or some kind of feature that clones the current state of the program??

[NoraCodes]

I was thinking of using the RustcSerialize trait for this.

[arces]

Checks to see if a player is in a middle of a non saveable event.

Things that saves:
Player Location
Events that happened
Current player/NPC stats (would override the default ones that load up)

[NoraCodes]

I think this is going to be the primary driver between game state/engine state separation, where the game state is information about the game world, while the engine state is information about the technical details that act on that information and display it to the user.

All the things you listed would definitely be in the game state category.