To give ds the remains of his packed lunch for his tea.....

[whoops]

Before giving him anything else to eat as I am fed up with throwing the contents of his lunch away
He normally has school dinners but today they had a picnic for their seaside topic. He chose what he wanted in his lunchbox and that's what he got but all he has eaten is the crisps and biscuit.
AIBU to make him eat the sandwiches before he has anything else to eat?

No

Nope, not if they're still ok.you could have your own picnic with him (and the sandwiches!)

Not at all. DD always comes out of school claiming she is 'starving'. I make her finish the contents of her lunchbox on the way home before getting anything else.