Here's a good tip I read on another web page:

Aftermarket rims, almost always come with a new set of wheel nuts. These new nuts often are not shaped the same way as the stock nuts. This could cause you some problems when trying to use your spare. Be certain that you can actually uses these new nuts with your spare. Make sure that the contact points conform properly to the indentations in the rim of the spare. If the new nuts do not work with the spare, take five of your stock nuts, wrap them in a plastic bag, and place them on top of the spare in the trunk.