My Grandad just passed away, how should I react?

After my grandfather died, for some reason I didn't really think anything of it till two days after. I guess something like that just doesn't seem like reality until we actually wake up from our sleep a couple of times. I think you should let your dad know that things will be okay, & even if you aren't religious, saying "He's in a better place now" Is comforting. So, maybe say that. Also, flowers & a card might brighten up the day.