Stop printing one dollar bills and only make one dollar coins available for circulation.
I was at the metro stop and saw an advertisement encouraging the use of dollar coins. Part of the message was that using coins saves money because the coins are more durable.
It struck me that if we want people to start using coins instead of bills, we could simply stop printing dollar bills and only make the coins available. In addition to savings associated with more durable money, there would be additional savings associated with eliminating a media campaign that would no longer be needed to promote the use of the coins.
A related suggestion is to eliminate the use of pennies. If it costs more to produce pennies than they are worth, we should stop producing them. Austratlia use two-cent coins instead of pennies.