Funny thing, actually. Any class can use any weapon, armor, or shield, it's just that you take penalties. Which means there are end-runs available. * If you use a weapon you aren't proficient with, it's a -4 to attack rolls. Our party wizard has handed his familiar a crossbow or a pistol to perform coup de grace attempts on targets he has hit with color spray: since a coup de grace is an automatic hit, the -4 proficiency penalty doesn't matter. * If you equip an armor or shield you aren't proficient with, you take their armor check penalty on your attack rolls and on all movement-related skill checks. Bucklers have no ACP, so any class can use one without penalty. It's also possible to fit an armored kilt to anything up to masterwork studded leather (or a mithral chain shirt) and suffer no attack roll penalties. Our wizard wears haramaki with an armored kilt for +2 armor AC with no penalty.