We all used raincoats and umbrellas, but only a few elders wore the overshoes. You can probably get some from the spare clothes closet if you decide to use them. At any rate, it's important to have comfortable shoes because your feet get hammered in the mission. Lots of us wore those lightweight Rockports with Vibram soles. Around the apartment people wore slippers, Tevas, or Birkenstocks.
Some people like to get one at the end of their mission.
You can buy a lot of other clothes too, but that puts you at risk of becoming a real burden during transfers. Almost all food in Italy is outstanding. I was served some strange things on occasion, including various innards, snails, raw octopus and other goodies. But with most people it's ok just to say you can't eat something if you really think it will make you ill. During my mission I grew to love tomatoes, olives, and other things I had hated before, so I would recommend trying new things as long as they don't make you sick.