Get a part time job in a paint store, or paint department of a home improvement store - just tell them your entire reason for being is to lift 2x 5 gal paint buckets across the store and out to customers cars... then unload pallets of said 5 gal buckets into the bays when trucks come in.
I'm only joking a little here, you use the same muscles and full 5 gal paint buckets start at 70ish lbs.