But not too many strawberries.

The verse shows him recognising that he has no hope of regaining his lost love. There is no more chance of that happening than there is of finding strawberrries in the ocean, or ships deep in the forest. Best he can hope for now is to die and be buried and be done with all that.

The verse has a very effective narrative quality. Economical and elliptic. And it also implicitly paints a picture of him wandering in the forest where the strawberries do grow. It's an extraordinarily powerful son with layers of meaning, and yet very simple.