Been there and done that! I had a bunch of pennies left over from a 5 gallon jar that sat in our family store for years. People would drop their extra pennies in there. I spent two winter going through there and found only a few good coins
My advice:
1. Get a 3-5x lens (I think my eyes got worse looking at all those pennies)
2. Do this in the winter night - summer is for being outside!!
3. When you are done with a few pounds - take them to the bank; don't do it all at once! They get a little upset when you walk in with $200 in copper.
4. Get the "Cherry Pickers Guide"
However, good luck looking!!
You before looking:
You after a few days:
You after a few weeks:

- notice the larger eye from squinting so much
You after a month of looking:
You after you find that great error coin!: