Yes, there is free lunch at Mayo Clinic Medicine Grand Rounds

And it improved attendance by 38.4% in a recent study published in BMC Medical Education. Pharmaceutical industry support was used to help defray the costs. The authors felt they addressed any ethical concerns about industry support:

Industry support of MGR raises the ethical concern of industry influence over MGR organizers, content, speakers, and attendees (1-3,17,18). This concern can be addressed by using the following guidelines: 1) industry support should be unrestricted; 2) MGR speakers should disclose to attendees any conflicts of interest; 3) industry representatives should not determine MGR content; and 4) presentations at MGR should be unbiased, especially when the industry sponsor’s products are discussed (3,19,20). These guidelines are rigorously followed at our institution.

They concluded:

Providing free food may be an effective strategy for increasing attendance at medical grand rounds.