I’d say start adding in berries as long as they are fresh. Wash them thoroughly of course. Don’t eat them if too old. Blueberries stay good for a long time.
I eat a green apple everday currently and it hasn’t been problematic for me whatsoever.
I’d also consider trying out fresh almond butter with celery as a snack and see if you get any reactions.
If you still get food reactions to any of these, I would try to heal leaky gut some more before proceding. For me, once my food reactions went away, I didn’t notice any detriment from eating these foods.