Continuity mistake: When Kimble goes back to the hospital as a janitor to check the hospital computer, the lady working in the lab is wearing two different dresses. (01:05:15)
Visible crew/equipment: After Sykes shoots the Transit Cop on the "L" Richard pulls the emergency brake, and in the following shot facing Richard as the train screeches in flashes of darkness, the reflection of a crew member quickly becomes visible on the glass window beside Richard. (01:47:45)
Continuity mistake: Kimble dives from the top of the dam when Gerard traps him in the tunnel. But in wide shots of Kimble falling, there's no tunnel above the dam. (The tunnel scenes were shot in Chicago, but the location sequences were done at Cheoah Dam in North Carolina - which has no tunnels. The end of the tunnel from which Harrison Ford supposedly jumped was built on the back of a large flatbed truck which was driven out on the top of the dam for the scene).
Answer: It's a cold compress. You squeeze it, and the inner bag breaks mixing chemicals and it gets very cold. It helps to minimize swelling. He gave it to Kimball for all the bruises he had.
Grumpy Scot