Campa (Carlos Gallardo) shows up to the firefight with a pair of guitar case machine guns. Robert Rodriguez has commented that the guitar case machine guns were built from MAC-10s.
Guitar Case Rocket Launcher
Quino (Albert Michel Jr.) brings a rocket launcher inside of a guitar case to greet Bucho's men.
Ponytailed gangster in bar scene. It has pearl grips.
Wildey
El Mariachi (Antonio Banderas) carries a scoped Wildey Magnum pistol in his guitar case. One of Bucho's hitmen also carried a Wildey Magnum in the movie.
Sawn-Off Shotgun
El Mariachi (Antonio Banderas) can also be seen firing a sawn-off shotgun 12 gauge. The magic of movies allows him to fire up to six shots from only two barrels before reloading.
Bucho (Joaquim de Almeida) seems to have a taste for exotic pistols, the Beretta 93R he carries is a very rare version of Beretta's popular 92FS model capable of 3-round burst fire. Bucho (Joaquim de Almeida) passes his 93R to Zamira (Angel Aviles) who makes use of its burst fire capability in the attack on Navajas (Danny Trejo). The Beretta 93R is later reused by one of Bucho's henchmen who fires at El Mariachi as he jumps from the roof of Carolina's (Selma Hayek) book store.
Codpiece Revolver
Although we never see the codpiece revolver fire it's one of the few firearms in the film with dialogue devoted to it. This same codpiece revolver was later reused by Robert Rodriguez in From Dusk Till Dawn.
Unknown Revolver
The Tarasco bartender (Cheech Marin) fires a suppressed revolver of unknown make and model.
MAC-10
Most of Bucho's (Joaquim de Almeida) men are armed with suppressed MAC-10 machine pistols that are most prominently featured in the Tarasco bar shootout. You will recognize the scene between El Mariachi (Antonio Banderas) and Empty Gun Man (Diego Sandoval) as inspiration for a similar scene between Agent Smith (Hugo Weaving) and Neo (Keanu Reeves) in The Matrix.
In the shootout at the Oro verde bar in Saragosa, El Mariachi pulls out a Sentinel Arms Stryker 12, along with the sawed off 12 gauge, that Buscemi described as "The biggest hand cannon I've ever fucking seen." This is the gun that is launched into the air and grabbed by El Mariachi right before the shooting starts. Sadly, this is the only instance in the film where this gun appears.