I would just keep offering. Maybe he finds the dry crackers easier to pick up? You could offer similar things such as toast fingers, pitta bread, naan or tortilla fingers, whilst they are still carbs foods they would still expand his experience. Do you ever roast veggies, you can oven bake with or without a little oil and they will be drier on the outside (and crunchy such as roast potato) and soft on the inside.
If he isn't too interested I wouldn't go to too much trouble preparing lots of different finger foods for him, I'd probably just offer something suitable from the family meal so you aren't cooking twice. He may also be more interested if he sees you eating the same thing, at the same time.