Those are Allparts oil & paper caps. They're an unnesessary expense, but it's kind of fun to play around with parts. If I really wanted to sink money into parts that don't sound that much better, Acme sells reproductions of Bumblebee caps, and those look a lot cooler. I think I'd want to do a hull hog '50s rewire before I'd buy those, where the braided cable from the jack goes all the way to the switch. That might be fun to try sometime.
Pete