I would chew my nails down to the quick with boredom I suppose.
Seriously, probably get more exercise, write more letters, watch more TV, do more household chores, more lawn work, etc. Read more, of course. Listen to more music. Do what I did before 2001 when I first connected to the 'net.
If you are talking about if the Internet had never been invented, how can you miss something if it never exists? A person would just then live their life.......same as saying what would you do if the TV did not exist, or the automobile, or telephone.