I LOVE the Green Toys brand tea set. It holds up to water, sand, paint, etc., and is easy to clean. It's a different type of plastic than many of the others I've used and is really sturdy and feels nice.
As far as a doctor kit, I haven't found any actual toy kits that hold up well. I've had more success with actual items and loose parts for this purpose. Medicine syringes (just make sure there's no rubber seal on the inside), popsicle sticks, empty bottles of different shapes and sizes (no lids for toddlers), lengths of cotton muslin or ace bandages, that kind of thing.