Food-stealing 5yr old

[lecce]

Ds has recently started helping himself to food and it is getting very annoying. The dc have to ask for snacks, but he has just decided to go for it. We don't keep 'junk' in the house, so it is mainly things like oat-cakes with marmite/peanut butter, rice cakes and fruit.

It bothers me because it often leads to his not eating well at meal-times and I find it a bit sneaky. The fruit annoys me because it tends to be more expensive items like blueberries etc that he goes for. I will think I have plenty for a packed lunch, then I find there are 5 left. Today was the worst incident yet - he has sneakily eaten a whole punnet of raspberries. Surprised he hasn't got an upset tummy and cross as no one else got a single one.

I have told him off, giving the reasons above for my anger, but what else can I do? We try to go for natural consequences, but I'm not really sure what those would be in this case. Btw, he can reach our highest cupboards on a chair, and I don't want locks as I feel that avoids the real issue.

Thanks for any advice.

(My dd is 18mo so no real life experience, so feel free to ignore me!)
Is there anyway you could portion off an amount that he can help himself to if he's hungry? So main punnet of raspberrys, next to that a pot with a coloured lid (so he knows it's his?) with 5 or whatever raspberrys in that he can eat when he wants?
The portioning means that you can 'ration' how much he's having to save some for everyone else as well as still ensuring he's hungry for main dinner times?

I'm not entirely sure where I stand on children having to ask for any and all snacks, but maybe have a pot of 'allowed' snack, that he can have whenever he wants, and if he wants anything that isn't in the pot he has to ask?