DS turned 15 during strict lockdown, we gave him £100 and I went wild with £10 in the Poundland chocolate aisle. You can get A LOT of chocolate in there for a tenner.
He was perfectly happy with that and saved that money and anything else he has acquired since then and just bought a guitar that he spent months looking for. I think just the feeling of having quite a bit of money to spend as he wished was a great present for him and he enjoyed the freedom of choosing how to spend it.