Plastic Easter eggs are common and cheap, around Easter they can be found at almost any store, and they can be ordered online year-round. Plastic eggs also avoid the issues of blowing eggs. They are also more durable then a blown egg and never spoil. These factors recommend them as a canvas for the Egg-Bot. There are a few limitations however. The first limitation is that the plastic is less receptive to ink than eggs and some inks have a tendency to wear off with handling. The second issue is the seam in the center of the egg.
The smooth plastic surface of the egg can be handled by a combination of pen speed (slower) pen choice and allowing the egg to dry undisturbed. A clear varnish can also help.
Plastic eggs have a joint at the widest point (the equator) where the two halves meet and usually have small plastic hinge that holds the two halves together. If the two halves meet well, it is sometimes possible to draw across the boundary of the halves. The hinge usually sticks up far enough to catch the pen and cause major alignment issues. Even under the best situations, drawing across the half boundary causes minor alignment issues. A simple and effective workaround is to design plots that only cross the equator while the pen is up. If plots are designed so that the equator is crossed only a few times, the hinge generally does not cause an issue.