Put the cider vinegar, sugar & salt in a large saucepan and bring to a boil. Stir to combine the sugar and when the sugar is completely dissolved, remove from the heat.
While the pickling mixture is heating up, peel the carrots and cut them into long planks - about ½ inch by ½ inch, do the same with the daikon. For the cucumber, I leave the peel on, but slice it in half, take a spoon and scoop out the seeds and then slice it into planks also. Keep the length uniform - I made all of the planks about 5 inches.
Add the planks to pickling liquid. Cover and let sit for 10 minutes. After 10 minutes, remove the pickles and put them into a glass jar - cover with the pickling liquid. Seal tightly and refrigerate.
The pickles will keep in the fridge for several weeks.