score:6
This is a shopping question, which isn't usually allowed on travel.se BUT, since there is only one thing everybody visiting Cambridge should do, I'll answer. What everybody should do when visiting Cambridge is Punting.
(Source: Wikicommons)
What to do else really depends on personal preference. I would suggest to resort to Travel guides (e.g. Guide Routard, Lonely planet, etc) or sites like Tripadvisor for ideas.