have/keep (all) your wits about you

to be ready to think quickly in a situation and react to things that you are not expecting. - avoir toute sa tête

• Cycling is potentially very dangerous in the city - you have to keep your wits about you.

Usually, wits.

• intelligent observation, keen perception
  using one's wits to get ahead.
  Synonyms: cleverness, cunning, wisdom, insight, perspicacity, sacaciousness, acumen.
  
• mental faculties
  to lose one's wits; frightened out of one's wits.

• scaring the wits out of: tout à fait effrayant
• to pit one's wits against sb: rivaliser d'esprit avec qn
• to have one's wits about one: avoir toute sa tête
• to pit one's wits against sb: se mesurer à qn
• to keep one's wits about one: garder la tête sur les épaules
• to frighten the wits out of sb: faire une peur bleue à qn
• to use one's wits to do sth: se servir de sa tête pour faire qch
• to gather one's wits: rassembler ses esprits
• be scared out of my wits: être mort de peur
• to engage in a battle of wits: jouer au plus fin
• to be at one's wits' end: ne plus savoir que faire
• wit: esprit,intelligence
• dim wit: imbécile
• dry wit: humour pince-sans-rire ; humour caustique
• Syn. : deadpan.
• half-wit: idiot
• quick wit: vivacité d'esprit
• ready wit: caractère spirituel
• flash of wit: boutade