We went cat-supply shopping at Tabby's Place and honored our Tucker by donating one day's worth of litter for all the cats. Litter is such a basic need that it only seemed right. :-)
The shopping process was quick and easy (well, it was quick AFTER I decided what to buy. They have the neatest giving system I've ever seen. You can even buy virtual gift baskets of cat supplies!)
Again, thanks to everyone who commented!