As the game develops, you'll need to plan to have some nice in-game debug and testing tools.
Command Console - Similar to the consoles in many games, this would allow developer and testers alike to poke and prod the game in various ways to squeeze out those bugs. Character, Inventory, and Environment state editing options, and few action commands (kill, spawn, move, etc..) would be very useful.
Logger - Being able to turn on a logger to write out the flow of the game functions would be very useful. I've made a few threaded asynchronous loggers in a number of C# applications to catch all those annoying bugs. Also having a logger allows testers a bit more ability to help the developer to hand in a log file and give a base level of information about the issue.
A few associated editors would be nice, too. But those can come at a later point.
