when i leave a country with non-euro curreny, i usually have a few coins and maybe a bank note left. when i return, i sometimes even remember the place i’ve put the stuff and take the money with me. the first bus ride could be paid with it.
however, you should make sure in advance that the bank notes are still valid and accepted! for the above shown blue note the case is obvious.
but one might expect that a five-year old czech 50-crowns-note (2€) will always be welcome, especially as a tip in a restaurant. but the waiter suddenly made clear signs of rejection and did not touch the note. completely puzzled and wondering what the czech tip policy might be, our local friends later explained me the situation: as also more resistant 50-crowns-coins do exist, the czech national bank abolished the notes in 2011.
by the way, my pasta was delicious. is left a few coins on the table.