Einmal hin, alles drin.
This is the motto of Real.
I know it means that you go to Real shopping for one time, you can get all you need. Are "hin" and "drin" single words or prefix?

I know in some mottos, people usually use brief expression and omit some verbs. But that made me not understand the grammatical structure of the sentence, could you give an example of the full sentence without omission ?

Question

Einmal hin, alles drin.
This is the motto of Real.
I know it means that you go to Real shopping for one time, you can get all you need. Are "hin" and "drin" single words or prefix?

I know in some mottos, people usually use brief expression and omit some verbs. But that made me not understand the grammatical structure of the sentence, could you give an example of the full sentence without omission ?

Answer

Ein Mal (dort) HIN GEHEN. Einkaufen. Und alles ist (IM Wagen oder IN der Tasche) DRIN.

hin: hingehen (to go somewhere)

Andere Bedeutung: 
"hin und her": durcheinander, Chaos, Unentschlossenheit
(to move) back and forth, not knowing what to do

Und noch eine Bedeutung:
hin: kaputt. "Es ist hin! (/hinüber)": Es ist kaputt /defekt /nicht mehr zu gebrauchen.

drin: darin, drinnen, innen, innerhalb (inside, within)

Dieser Satz reimt sich. Die Hörer werden den Satz ergänzen können.
This sentence has a rhyme. The audience will be able to complete the sentence. 
hin - drin
hingehen - drin haben.