The only things you need are:
4 cups vinegar (white, but I've used half white vinegar and half apple cider vinegar before)
1-1.5 cups sugar (or to taste)
cracked pepper (to taste)
Slice it all up, add it all together, and let the juices soak into the veggies overnight. You can add more or less sugar to the mix, it cuts the bitterness of the vinegar but you don't taste actual sugar so as little as you can handle will make it better for you. Serve as a side, a snack, or just leave it in the fridge and I bet it will be picked to it's death with someone asking for more when it's gone. This picture doesn't do it justice, but it will have to do (I brought some for lunch today, hehe)....
WARNING: One downfall to my new love for onions is my newfound onion breath. Onions mixed with vinegar tend to accentuate that debacle so DO NOT eat this before a date, or any time you will be within a foot of someone else's face in the near future. Otherwise, enjoy :)