Pretty sure this is Neon City (1991).
Neon City (also known as Anno 2053 in Italy, Neonski Grad in Serbia) is a 1991 Canadian post-apocalyptic science fiction film directed by Monte Markham and written by Jeff Begun and Ann Lewis Hamilton, under the pseudonym Buck Finch. The cast includes Michael Ironside, Vanity, Lyle Alzado, Valerie Wildman, Nick Klar, Juliet Landau, Richard Sanders and Markham.
In the 2050s, extensive ecological damage has resulted in largely lawless areas that are controlled by mutant raiders. Harry Stark, an ex-cop who now works as a bounty hunter in the wastelands, saves a woman from mutant outlaws. After she pulls a knife on him, he knocks her unconscious and brings her back to town for her bounty. Captain Raymond, Stark's former commanding officer, tells him that the woman, Reno, must be brought to Neon City to collect his payment. Raymond requests that Stark ride shotgun on a transport that is going to Neon City, but he refuses. When Stark's truck blows up, Raymond claims it to be an act of terrorism by mutants. Stark attacks Raymond, only to be knocked unconscious and placed on the transport with Reno.
On board the transport are Bulk, a former friend and ex-cop whom Stark once arrested; Tom, a serial killer who pretends to be a doctor; Dickie Devine, a clown; Sandy, Stark's ex-wife; Twink, the sheltered daughter of an influential Neon City politician; and Wing, an old man who keeps to himself. Before they leave, Raymond gives them the opportunity to receive a refund and stay behind, as mutant activity along the road has been excessive; all elect to go instead of staying and collecting a refund. Along the way, they pass through a deadly Xander Cloud, and, when they stop afterward, they meet a family who is suffering from extensive radiation damage. Stark buys a euthanasia kit from Devine and donates it to the grateful family. Disgusted, Reno calls Devine and Stark no better than herself.
The aforementioned "euthanasia kit" is a small bottle of poisonous red liquid, kept in a little bag. You can view the relevant scene at the 37:01 mark in the video below.