Man does not live by bread alone

Meaning

Physical nourishment is not sufficient for a healthy life; man also has spiritual needs.

Keep your powder dry

Meaning

Be prepared and save your resources until they are needed.

If you can't stand the heat, get out of the kitchen

Meaning

Don't persist with a task if the pressure of it is too much for you. The implication being that, if you can't cope, you should leave the work to someone who can.

Beauty is only skin deep

Meaning
Physical beauty is superficial.

Don't keep a dog and bark yourself

Meaning
Don't pay someone to do a task and then do it yourself.