Early in the Morning
The official name for this day is Here We Go 'round the Mulberry Bush Day, but no one ever uses the full title anymore.
This is an obvious reference to the children's rhyme that goes like this, in case you're unfamiliar with it.
Here we go 'round the mulberry bush,
The mulberry bush,
The mulberry bush.
Here we go 'round the mulberry bush
So early in the morning.
Exciting stuff, no? Well, that's what you get to do today to celebrate. Find your nearest mulberry bush and go 'round it.
It's best if you can (as was intended for children to do) find several friends or acquaintances to do this with you. All hold hands 'round the bush and skip counter-clockwise as you sing the ditty above.
If you're not sure of the melody, you can check out one version here. This one gives you several bonus verses, but I think some of them are modern additions not found in the original song.