A Fendi Baguette bag customized by Jeff Koons.

HAMMER TIME: A new frontier has broken out in the luxury handbag wars — and it's all for a good cause. Rare and collectible Fendi and Chanel purses will be among items auctioned off by Sharon Stone May 22 at the amfAR gala during the Cannes Film Festival. Silvia Venturini Fendi really went to town, creating a plain white canvas baguette and inviting 20 art world stars to customize them in aid of various charities. Participants include Jeff Koons, Kendell Geers, Francesco Vezzoli, Subodh Gupta, Sylvie Fleury and Tom Sachs, who painted his black, signed it and noted, "Please Display Other Side." Meanwhile, at Chanel, Karl Lagerfeld went full-throttle luxury, creating a lustrous alligator style with a double-C clasp pavéd in 334 diamonds.