Item and character duplication
This trick is best to do at the main menu or at a Training Hall.

First save the game. Now remove one member of your party, so you have five. Then create a new character, for example "Bob", and add him in. Take off all of his equipment.

Transfer all the equipment you want copied to Bob. Remove him, and quit the game do not save the game.

Reload that game, and you will be back to your original six party members, with the items you wish to copy. Remove that character once again, and add in Bob, and he will also have those items. Trade those items back to the party, and your party will have their items, and the items that Bob had.

Now remove Bob and add in your other members, save, and you will be back into the game, with two sets of items.

The character duplication trick is easier, but only if he or she has not been in a fight and can be changed. Rename your character using the "Modify Character" command, then remove him or her. Quit with no saving, and reload. Your renamed party member will be in the pool of characters, and your first character will still be in the party. This is also a neat way to gather up useful items from new characters in Dark Queen of Krynn, where a few of them receive potent magical items not found in Death Knights of Krynn.