money storage problem

[36mum]

My 12yr old son is going to a theme park next week with school. He is very good at losing and forgetting things do I want him to take the bare minimum with him. I don't want him to take a bag because he will leave it somewhere whilst on rides and forget. He has ADHD which doesn't help.

Does anyone have any ideas how he can store spending money and his cheep small phone ?

Money belt like holiday can get thin under clothes one or more belt type things.

Or search arm wallet get something like this big enough phone and money