A transactional Database with a web user interface or Access Database with Visual Basic etc for the user interface to shared database is easiest method in which a report can be generated in the end with all sorts of info. You can basically make an internal point of sale system, generate a report that has the order info, fax this to caterer after printing it, and then perform another print out that has everyones orders by department and that then would be broken down into employee names with totals due etc. Also would be beneficial to add a certain percentage to cover the tip to the caterer etc.
Then your only left dealing with making sure everyone paid
The biggest reason why you need it to be a transactional system is because if everyone is in say an Excel order form document 2 people open at the same time to the shared location by which this single document resides, Bob orders his Sub and saves and closes the worksheet order form, and then Doug edits his copy and then saves his order, Bobs order is now gone as for Dougs information overwrote Bobs changes.
HTML Forms are a good interface for users, but you would need to have a system to handle all the information received, and options to handle this information are ( send to e-mail or send to database ) pretty much. And the send to e-mail wouldnt help you much since thats the issue you have now.
Does your workplace have somone able of creating a transactional database for everyone to access through a neat user interface with drop down menu's etc of what the caterer can create? If you do, your all set. Otherwise I am not sure if anyone here would make one for free or not. Its a pretty involved project to make interface for the menu and then the database.
Its too bad your caterer doesnt make a website with ability to order. If they already have one, then see if they can add a feature for your company to process group ordering.
I use to support a food store chain that had a catering department and supported a product called Cheftec, a program for keeping track of the Catering Department as well as processing orders. Problem is that its not cheap software and requires to be installed on a server with SQL database.