They had monthly pocket money for treats, sweets, comics etc.
If they wanted expensive trainers or similar I would tell them how much I would spend on a non branded pair and agree to put that towards their purchase but they had to make up any difference from birthday/Christmas money. That really made them think about how much they wanted something and whether they wanted to part with their cash or not.
At secondary school I gave them a monthly amount that equates to the cost of school dinners for the month. It was their decision is they had school dinners or chose to divide the money into weeks and buy the food to make their packed lunches.
They mostly chose the packed lunch option and we would go to the local supermarket where they would buy their food for the week, quite often pooling their money to take advantage of offers etc or sharing a 6 pack of bread rolls.
This really helped them with both budgeting and meal planning and they loved getting a deal or a bargain. They could keep any of the money they had left over and used to treat themselves to an ice cream from the van outside school on a Friday.
I'm proud to say they never ran out of money, they just enjoyed the challenge but I did say to them if they ever did run out, there was bread and ham in the fridge and an apple in the fruit bowl, but I wouldn't top the money up until the following month.
They never struggled at Uni with food shops or budgeting or indeed cooking and I think it worked really well.