As an Sales Representative, I want to see the last time a Contact responded to a Campaign.
You can rollup the Date of the last Campaign response to a Contact record via Campaign Membership.
First, Create a custom date field on the Contact record (Campaign Last Response Date) and then, from the Rollups tab, select New.
Select Contact as the place you would like your results to reside.
Select your custom field (Campaign Last Response Date)
Select Campaign Member with the relationship ContactID - CampaignMember.ContactID, then select First Responded Date at the Field on Campaign Member to use as a source. Select Maximum, then either Save, or Save and Run your rollup.