It depends which kind of rubber tees you mean. Like a driving range tees, then no. But you can use the pyramid tees that usually come in a bunch of three in three different sizes.
I can't give an answer for all tees, but yes rubber and plastic are materials that tees are made from. The key thing is to make sure they are passed for play by the USGA and R&A.
Generally rubber and plastic tees are legal as long as they have been approved by Golf's ruling bodies. I can't give you an answer for all because some are legal and some aren't.
Depends on the size of the golf tees.
There are a few stores that offer printing of personalized golf tees. One purchase personalized tees from 'The Golf Tee Store', 'Golf Tees Etc' and 'Golfers Shop Here'.
18...people keep extra tees in their golf bags though...but there are 18 ON the golf field..as you call it.
there is no such thing
Clubs, tees, balls.
Clubs, balls, tees and a bag.
Yes, they are an accessory.