I'm a fan of the mortar and pestle when it comes to pills especially, but i suppose it would work quite nicely with coke too. Make sure not to get one that's porous though, a lot of them are. If you can find marble, that's the best in my personal opinion. Its a little "slipperier" than finished wood, which also works well. I've never used it for coke but for pills... top notch. Also, one of those prepaid phone cards works really really well because there are no indentations, they're about as stiff as a normal credit card too but only about 1/2 the thickness.