I don't normally like raw carrots but the pre-pepared 'baby' carrots they do in Asda (don't know where else) are really nice. Otherwise, prepare carrot batons, put in a glass of water in the fridge to crisp up.
Def try the sugar snap peas, fun to pod and eat (in summer try to get some fresh normal peas in the pod too).
Are there any salad leaves he might contemplate? My non-veg loving DD likes the crisp stems of romaine lettuce.