I know this question is a little old, but I was using the search function for some similar help and stumbled across it - I saw you'd had no response.
My DD (7) has just has this diagnosis after a negative test for Coeliac disease and the GP has recommended a low fibre diet as she has been getting a lot of loose stools (not quite liquid, but very loose and pale) and severe cramps - she has missed loads of school :( .
She has Mebeverine to stop the spasms (partial success I suppose) and Imodium to try and stop the runs! This has not started working yet as we've only just started.
I suppose white bread, white pittas, white wraps, white pasta (get the picture!) or cream crackers with cheese/ham/chicken would be ok in lunches.
I think it's going to be tricky as we generally eat a higher fibre diet as my older DD is more inclined the other way IYSWIM?
I think the type of diet depends on the type of IBS, those inclined to diarrhoea (sp) benefit from low fibre and those inclined to constipation need more fibre, but I think it should be soluble fibre rather than insoluble, although I'm not too clued up on the difference.
Hope you find some good lunch ideas, please post them if you do!