I have some thick (3/4") cardboard*, that the lathe came in, that I cut to fit the rotary table and the mill table extensions.
These have proven satisfactory for the 3 years I have been using my shop.
{Would not be ideal if you are using water based coolant/lube, but I only use oils.}
Alternatives:: plywood, foam, laminate, tiles
If you can put alignment rows under the material, so much the better.