Supply models and I'll have a go at the energy drink.
Bonk does not make you invincible. Explosions and area-damage weapons like the flamethrower will still affect you AFAIK.
Sentry guns will not damage a Scout under the influence of Bonk!, but he will still experience knockback. If a scout is set on fire while he drinks Bonk!, he will not take damage from furthur flamethrower attacks during the invicibility mode but he will continue to burn from the original fire.