A better option to freezing radishes is dehydrating them and then storing them.Green Onions: Flash freezing is recommended for green onions. This way you can pull out just the desired amount instead of an entire clump of green onions. It probably isn't a good idea to use previously frozen green onions in a salad because their texture would be tough. So just slice, freeze flash and put into Ziploc bags and freeze. Simple enough for me!
Carrots: It is best to freeze carrots after they have been cooked. You can blanch baby carrots in boiling water for about 5 min and strips or slices of carrots for about 2 min. Cool them in ice water. Drain and then store in Ziploc bags. You could also mash them up to make a great homemade baby food.
Watermelon/ Cantaloupe: I was surprised to find that freezing melon works great! You need to cut the watermelon away from the rind and make sure the seeds have been cut out. Slice or cut it into wedges, cubes or balls. You can then flash freeze it and store it in Ziploc bags. I learned that eating it frozen is amazing, but if you let it thaw out its not so great. You can also freeze the melon in a syrup to retain it's sweetness. Here was a great website I found that had a great syrup recipe.