You know the school as you attend there and if you are not offended because you recognize their good intentions then I will not be offended. I am blessed in that I don't have to eat with 'austerity' in mind but many people do. I agree that for many that means canned food and that means just whatever random thing can be provided from a food bank. Perhaps an actual food drive where students actually bring in nonperishable food to be donated to a food bank would be actually more helpful. If a student at your school doesn't have a family that has to budget for what they eat I'm not sure that having an austerity lunch on occasion really shows them what it is like - its just a lunch of jacket potato for them. If there are any people at your school whose families do have to be careful on what is spent on food (eating in austerity everyday) the school lunch is probably the most nutritious meal for them and it is a shame that they have to miss out on that meal. But, if I'm being honest, is the school actually trying to teach lessons here or are they simply implementing cost saving in their own budget by occasionally providing a less expensive meal for their students? Is there any documented evidence that the 'money saved' has gone to a school charity?
I feel there are plenty of good families who have to eat meals based on austerity but austerity doesn't necessarily mean a family lives in utter poverty either. It means they have to be selective as to what they buy but for some that means as previously stated food from the food bank.
My personal opinion is that it's really a cost-saving strategy for the school and they are putting a good deed name to it. Perhaps I'm wrong though and it really is in trying to educate students on needs of the less fortunate but I'm not sure an occasional meal of a jacket potato really drives that message home. Just my two cents.
I'm sure your school is very good though (I mean that sincerely, btw) and if you genuinely believe it is coming from a place of good intention then it is not up to us to judge.