Use the fork to scoop out the center of the top of the bun, leaving about 1/2 inch on the sides and 1 inch on the ends.
On the cutting board use the sharp knife to cut four 1/4-inch-thick slices from the cucumber for the wheels. Use the knife to cut 2 thin carrot sticks, each about 4 inches long, for the axles. (Save any remaining cucumber and carrot and cut them up to use as vegetable dippers.)
About 1 or 2 inches from each end of the bun, push the drinking straw through the bun where the wheels will go to make holes for the axles. Next poke the straw through the centers of the cucumber slices. Throw away the straw. Slide the carrot sticks through the bun for axles. Attach the cucumber slices to the axles.
Stick a toothpick into 2 of the olives. Cut 2 slices from the remaining olive. Push a slice onto each toothpick behind the whole olive. Push the end of each toothpick into the front of the bun for headlights.
Fill the bun with the sour cream dip and vegetables. If you like, add a pretzel for a steering wheel. Makes 2 servings.