Thank you both for your suggestions and questions. The students that travel with our group are generally completely novice travelers. Often these students are taking their first plane ride or first steps out of the United States/North America.
I have considered issuing funds as "banker" but would have to acquire the cash and would myself be limited by the bank-machine rules. I don't anticipate having $500 worth of euros being sufficient to properly arm the students for the day, but it may be the best option.
In general our students actually tend to use debit cards more than anything else day-to-day. Although I've encouraged past student travelers to use ATM for a better exchange rate, many are from traditional lower-income families that prefer to send them with traveler's checks many do their banking with companies that charge them a lot to use an ATM and limit their withdrawals significantly. I intend to stress the need to use an ATM, particularly on a Sunday arrival, but anticipate a large portion of them to ignore or fail to absorb the importance of this.
We've brought the students to Paris before, but we've never arrived on a Sunday before, and that is giving me pause. Generally, our first day is spent teaching them to use Metro and trains (and making sure their passes work), taking them to ATMs and banks or bureaux to exchange money, and getting them oriented to the city with a clues-based game in groups of about 10. After checking them into the hotel, they go out and about in groups of 3 minimum and are encouraged to limit their groups to six or so. They build their own itineraries with daily contact with staff members and staff members to help with emergencies (passport loss, medical issues, etc.)
Other groups from our campus, generally smaller in number, tend to keep the students together for a large part of their adventure; I prefer that the students experience things more personally, choose their experiences, and learn greater self-sufficiency. This method is more challenging when arriving on Sunday.
The need to set up catering is clear. I've done that before for London, but haven't had to do that before in Paris, so while large-scale events are normal to me, the location is not. So, I'm approaching this with some trepidation.