Literally, “empty sack does not stay standing”, or more loosely translated as “empty sacks do not stand upright”. The "sack" in the phrase is an allusion to the human stomach.
saco vazio não para em pé
- (Brazil) one needs food in order to function well.
Deixa o trabalho aí e vai comer; saco vazio não para em pé, cê sabe, né?- Leave your work right there and go eat; empty sacks don't stand upright, you know that, don'tcha?