Shrapnel is also a slang term for worthless coinage which comes into your possesion in the form of change from purchases, but is too small to buy or do anything with. For example, 5 and 10 cent coins easily fall into the shrapnel category, whereas higher coins are borderline since you only need four or five of them to buy something (like a can of drink, bus fare, etc).
Different people tend to manage their shrapnel in different ways. Some spend a lot of time actually keeping it, then counting and using it when the opportunity arises. Some just dump it all into a container at home and never do anything with it.
In some places, there are machines that accept coins for tickets, road tolls, food, etc. Many people love to use these machines to jettison their shrapnel by using the most number of coins they can (that is, using the smallest coins). This can be effective, depending on the machine, some don't take the really low denominations, some have a hard limit on the number of coins that they will accept.
While many people prefer to use the machines, some are a little more daring and will dump a few kilos of coins on an innocent human cashier, who will then spend a few minutes counting it afer giving you a look.
Whatever you do with your shrapnel, it can prove a frustrating part of modern, western life.