Wash the produce under cool running water just before you cut it. Scrub firm vegetables like carrots with a brush. Skip soap or commercial washes; water and friction are what food-safety agencies recommend.
Dry everything thoroughly. A salad spinner for greens and a towel for the rest. Leftover moisture is the main reason prepped vegetables turn slimy.
Cut sturdy vegetables first: carrot and celery sticks, pepper strips, broccoli and cauliflower florets, shredded cabbage.
Store carrot and celery sticks submerged in water in a covered jar to keep them crunchy (change the water every 2 days). Store the others in containers lined with a dry paper towel.
Dice onions for cooking and keep them in a well-sealed container (they're pungent).
Label containers with the prep date and put the ones you'll use first at the front of the fridge.