Most schools will let you know how much money to give for the trip.
Most of the time they will also tell how, cash, card or other methods.
How much depends on what they have to pay and you will like adjust the method to the amount.
If it is just a small amount, souvenirs and the odd snack, cash is still the easiest.
If the kids have to pay for lunch cash or a prepaid card.
I would not give a teen a credit card, certainly not without a limit on it.
But if your kid already has a smart way to pay, like a phone or watch, that might work.