Yikes - even with staples in my head, after my crani, I was able to wash my hair and shower within 2 days. In fact they wanted me to shampoo to get all the blood out of my hair.
I would definitely do the plastic with tape. There is waterproof tape you can get that will keep it out, and facing the shower will help.
I didn't have staples after my back surgery - dissolvable sutures were used.