Can you place 5 nickels in space so that each touches the other 4. It turns out that there is a well known solution in the case of pennies, but it fails in the case of nickels. The critical height-diameter ration turns out (with the help of Mathematica) to be 12.47, and this ratio for pennies is 13 and for nickels 11. But there are other ways of doing nickels.
What about beer cans? Drinking straws? When is there a solution that does not have a triple or quadruple point (a point at which >2 cylinders meet)?