Restaurant Passport

I've a client that is looking to have people sign in to their website and be able to gain access to a list of restaurants. These restaurants will be offering a special menu item, where if the visitor orders they get their 'virtual' passport stamped with a secret code. The visitor would then need to submit that proof of purchase to the client to qualify for prizes. What would you suggest for addons that could assist in the way of a series of mini forms for the visitor to submit, probably nothing more than name, email, restaurant code. Then the client could download the results via csv to tally the results.

Hope I'm explaining this well enough.

Custom form extension is probably all you'll need. Such extensions let you create custom forms to request information and store in custom databases. Suggest checking the Joomla extension directory for one that'd fit your needs as there's quite a few.