Robots are appropriate for any occasion. They are neutral but friendly so you can use this card for birthdays, get well soon, congratulations on your new baby, good luck on your exams, anything!
A classier kind of "hang in there" for modern times.
These cute little sticky notes sell for $3.50 at Nothing Elegant.
Sometimes you have complicated feelings to express and the only thing you can think of to convey said feelings is a hamster dressed as a lumberjack. Go with your gut.
I'd prefer to write a note on a real leaf with a sharp stick, but that's just me.
He doesn't really look like he wants you to have a nice day, but the sentiment is there.