This is so simple, if you didn't think of it already, you'll probably say "Duh" to yourself...

Personally, I like having a smaller party, so I go running around w/ 2 fighters, 1 thief, 1 cleric and 1 mage. You may want to consider the value of smaller parties not only because they gain experience quickly (I was averaging around 12th level by the end of the game on my first trip through...) but also because it gives you that open slot on the character arbitration board...what an excellent place to put a clone of that fighter who was holding onto all of the best items when you just happened to utilize the export button on the character stat sheet... I give my clones such colourful names like: "arrows, potions, scrolls, armour...etc. etc.

Be advised, however that you cannot perform character arbitration during the midst of a battle (sorry, they may let your characters turn into magic item factories but they won't let you have "Insta-Mage" at that crucial moment...)

Naturally after you export the character w/ all of the goodies, then you import him/her into the game (thus duplicating the items). From this initial duplication, it is not a far step to see the beauty of applying this "tactic" to stackable items. By duplicating gems or high-priced magical items, it becomes rather easy to have all the gold you want (of course you'll want to duplicate any high-priced items you buy and sell them back to the merchant you bought it from in the first place...)

I find that it is particularly useful to duplicate the potion of invisibility as well as any items that permanently increase your characters attributes. I'm not sure but I think the game randomly generates the magical item that you may (or may not)find, as I have only found a couple of attribute boosting items. If this theory is true, then the import feature is also handy in starting the game over (w/ the same characters)so that you can find those items that are eluding you...believe me when I say that the early part of the game is a walk in the park on the second time around (especially if your characters are blessed w/ a 25 Con...ain't regeneration grand?)