PICKLING LIQUID: Bring pickling liquid ingredients to a boil in a 3-quart nonreactive saucepan over moderate heat, stirring until sugar is dissolved. Transfer to a 4-quart nonreactive bowl and cool about 30 minutes.
VEGETABLES: Bring 6 quarts unsalted water to a boil in an 8-quart pot. Have ready a large bowl of ice and cold water, and a large colander. Add cauliflower to pot and boil until crisp-tender, about 4 minutes, then transfer with a slotted spoon to ice bath to stop cooking.
Cook remaining vegetables separately in same manner, allowing 4 minutes for carrots, 3 minutes each for bell peppers, 2 minutes for celery and 1 minute for onions. Drain all vegetables in a colander.
Add cooked vegetables, peperoncini, and olives to pickling liquid, Weight vegetables with a plate to keep them submerged, then chill, covered, at least 1 day. Transfer to jars. Refrigerate up to 2 or 3 weeks, if they last that long!