I have also found the amounts needed/used can be “seasonal”. Even though the school provides money for dinners on away game days (since they would be too late to eat dinner at school), there is often a need (want?) for more than the allowance covers - and certain seasons require further and longer travel so the incidences of eating out are more frequent. Some kids “order out” more in winter since the NE winters can be long and boring…
As @SevenDad says: it can depend on the school location and culture as well. I can’t imagine most kids needing any more than $100/month, but this is also dependent on what you are expecting them to “cover” with it. As @PhotographerMom said, a lot can be obtained at the school store!