Yes - that's kind of what I had in mind when I first suggested it. When containers fall of ships they often wash ashore on the UK coast. Even a container of motorbikes arrived in Cornwall recently... I'm presuming that only happens because they have some natural bouyancy.
Depending on contents, some might float very well. Or even dissolve away. My dollar store salt-shakers (with salt) came from vietnam.
The top will be the lightest containers, so I’m guessing that’s where your 40 footer of ping pong balls is sitting.