There are a number of things no dancer should be without:

Curative Salves (Arnica gel, Ben-Gay, Icy Hot, etc.)
Duct Tape (good for fixing shoes and pretty much everything else)
A Sewing Kit
Water
Band-Aids
Swiss Army knife or similar

You get the idea.

There are also a number of things you don't need:

A scale
Flip-flops

A scale is a worthless piece of garbage and if you have one at home, throw it away. The only people who need scales are athletes who need to make weight for a certain weight class, as in wrestling or boxing. Dancers do not need to know how much they weigh, they only need to know they are fit and healthy and a scale can't tell you this- it will only make you crazy.

Flip-flops. Take EVERY pair of flip-flops you have, EVERY SINGLE DAMN PAIR, and throw them away with the scale. NEVER wear a shoe that forces you to grip with your toes in order to keep it on.

But, I don't grip my toes, Jerry!

Yes, you do, and in ways you don't even realize.

When you're sitting down, you probably cross one leg over the other and absentmindedly bounce your foot up and down, unconsciously gripping your toes every time to keep your flip-flop from flying off and hitting some poor unsuspecting bystander. Every time you grip your toes, you are doing something that is SOOOOOOO bad for your dancing. You have to use your toes properly, and gripping them is not using them properly.

But, what will I wear?

Sandals with a heel strap, sneakers, ANYTHING that fits on your foot (and hopefully has some form of arch support) and stays there without you having to hold it by gripping your toes.

Say it with me: Gripping your toes is bad! LOUDER! I can't hear you!

Oh, wait, this is a blog... of course I can't hear you.

Well, say it anyway...

Seriously, though, if you have any intention of making ballet your career, you will spend 90% of your time en pointe, and wearing flip-flops will compromise your pointe work. Even if you are not going to dance as a vocation, gripping your toes tightens up your ankles and calves, and wearing shoes without support will affect your knees, badly.

Go now, young jedi, throw away your scales and flip-flops; you do not need them.

See you in class.