Hi Andrea,
Number one is correct (just one small typo in the word waisting = should be wasting). This is because the word "possible" at the end qualifies this as a superlative.
You can waste less food (Without possible) but with possible, you can only waste the least food.
"The less" that is in sentence number two is not gramatically correct in English.
Also note that arriving in this sentence is not really natural. The more natural way to say this sentence would be:
Everyone starting from producers to the end consumers should work on wasting the least food possible.