FREE: Looking for a basket /crate for my bike

Hello, I just learned biking. I am looking for a basket/crate (like a milk crate or similar basket that is solid and can be attached to back rack of the bike) to attach to the back rack of the bike. it would be nice something with a lock and waterproof if possible. So, I can use my bike more efficiently like shopping etc. Please, let me if you have something suitable for me. I live in Vic West area. Thanks Hunkar.