Last session I for the first time got to use bottlecaps for bennies and they were generally well received by the players: they're just the right weight, don't roll all over the table and are thematically a great match. I got the coca cola caps off of ebay (88 for €1). Inspired by the Sunset Sarsaparilla star bottlecaps from Fallout: New Vegas I added a pair of "lucky star" bottlecaps.
1: No luck, no bonus
2-15: +1 bonus to the roll
16-19: +2 bonus to the roll
20: Automatic success, "best outcome" unless the roll comes up as snake eyes. Up to the GM what the effect of a 20 exactly is, but the basic idea of it is that whatever the character was trying to do will succeed in the coolest possible fashion. ;)