My dd is going on a school trip for 5 days in September, when she'll be 10.
The spending money limit is...wait for it.... £1.50, total. Yes, one pound and fifty pence.
The school has done this trip for more than ten years, and this is their experience talking.
The reasoning is that they are going to an activity venter in the middle of nowhere, and the only thing they can spend money on is a vending machine for chocolate, so the £1.50 will be doled out at 50p a day on the middle three days, so they can spend it, if they actually want, during the free time of one hour they'll get just before evening dinner.
They'll be able to eat as much as they want at mealtimes, and this place has a good reputation, and very good cooks, there's a lot of variety.
And for the rest of the day, they'll be with someone at all times, no sneaking off, no mobile phones, just a lot of good, healthy, physical activities. Swimming, archery, biking, high ropes, kayaking, the lot and more.
In fact, I expect dd to come home skinnier, while I also expect she'll be eating like a horse the whole week.