Most of the produce items in your boxes right now are not washed between leaving the field and entering your house. Cooking at high temperatures, when applicable, is a reliable way to kill bacteria. For items you plan to consume raw, you should do the following, you should take the following steps to ensure they are safe to eat:
For Melons and Onions, washing the peels is not effective. Use a separate cutting board to cut through or remove the peels. Then rinse the peeled item before continuing to process it. Just remember that every time you cut through the peel and into the flesh, you can transfer bacteria.
For Watermelons and Cucumbers: Wash the peel with soap and water before slicing.
For Tomatoes, Stone Fruit, Zucchini, and Peppers: Rinse the fruit well before cutting. Use a brush to remove any dirt.
For Grapes: Simply rinsing will not get grapes clean. Fill a bowl of water with water and and drop the grapes into the bowl for a minute or two, then remove and rinse again with clean water.
Carrots and Garlic grow entirely underground, where pathogens like E. Coli and Salmonella do not readily spread. That said, it is easy to take the same precautions with them as you would similar vegetables.