Excellent vegetables can often be around closing time of food markets. It is also one of the most common things to find while skipping. If you pick it from a dumpster, look at it and smell it, then make sure to wash it thoroughly, and please don't eat it if it smells bad or is somewhat rotten. Wash and cut all bad parts away. Note that some veggies like potato can develop green parts which indicate the high level of natural toxins in vegetable - in such a case, throw away the whole vegetable.
Sometimes a diver's find can be so big that one might want to preserve veggies for future. Vegetables are perfect for freezing them, and then using them anytime for soups and other meals. You can also use them for "veggie shakes" mixing them with fruits in a blender - it is very healthy!