Forgive me if this is a really stupid question, but are there Latin words for modern things like computers, missiles, cars, telephones, text messages, etc.?
Indeed there are. Multiple sources, including the Vatican and Oxford, are constantly updating the vocab. You can find most of these words by going to Wikipedia, going to the article of your word of choice, and clicking the "Latina" link in the "other languages" table, or just going straight to Vicipaedia and looking them up.
Cell Phone--Telephonum Gestabile
Computer--Computatrum (Laptop Computer=Computatrum Gestabile)
Car--Autocinetum or Autoraeda or Automobile
just for example