Its the muffler for the smog system, and ive never seen it have a tube on the outboard end. On 100s of these trucks.It's a vent for the smog system that use to have a flexible aluminum tube that went out the hole right there in the metal inner support for the fender.
The plastic "coffee can" is the air inlet filter. The metal coffee can is a vacuum reservoir. The black box below the battery is the charcoal canister and it traps fuel vapors from the tank, and releases them into the intake when under load.