Helmets. . .defensive cycling. . .lights. . .bright clothing. . .maintenance.
Folks, there's NO SINGLE technology or behavior that's gonna' make cycling [or life] risk free. Every time we throw a leg over the seat we're throwing the dice. Every smart action we take only reduces the chance of throwing snake-eyes. Yeah, my helmet can't defend against many easily conceivable decelerations but I'll keep wearing it. . .it adds a few 'points' in my favor in the dice throw and THAT'S all I can ask of a Forgiving God [or a Cold Universe or Fate or Entropy].
300 Gs!! Holy-Moley!! I can't think of anything in my immediate environment that would generate that acceleration. 'Course, I don't get out like I used to.