Backing up Hana here - white bread has had some of the 'goodness' taken out so if you are eating bread then wholemeal and granary are usually better.
However many of us think that all carbohydrates are not a good thing for diabetics.
If you look at food labels you may well see 'Per 100g, carbohydrates 13.5g (of which sugars 2.2g)' [that was me reading off a label I have beside me].
So sugar is a carbohydrate and other carbohydrates transform to sugar quite easily.
So if possible a lunch should be maily based on protein and vegetables.
To help more, we would need to know what his likes and dislikes are so we can suggest which of the 'likes' could be built on.
Fats are also not necessarily bad, or at least not as bad as carbohydrates.
A lot of dietary advice about what is 'good food' does not apply to diabetics - fats suddenly become better and carbohydrates worse.
A lunch box with chicken breast, hard boiled eggs, cold crispy bacon, cherry tomatoes, cold sausage can be filling and low in carbohydrate.
Biscuits are not good, generally.
As in all things, any reduction in sugary and carby foods is a good thing.
It is very hard to go 'cold turkey' on carbs.
Oh, and cold turkey is a good lunch as well
Cheers
LGC