In episode 2, first page, after you beat the the skull on a stick and go down, kill the only creep in that room. After doing this, stay in the room and read the thought balloons for Sketch. He will say that the far wall looks weak, then walk over and punch it. The wall will break and you will be able to go in and find a health bottle, a knife, and a power fist.
When you get to Episode 3, drop off Roadkill the Rat in the first room of the cave in the lower left hand corner. A secret room should appear after you have killed everything in this room.