My old girl had epilepsy and pancreatitis. We tried Hills and Royal Canin prescription diets and she flatly refused them.
The only food she would eat and wouldn't get episodes with was the Prime single protein pet rolls - Kangaroo & Potato at about $11.50 per 2kg roll and boiled chicken breast.
Any kind of treat, scrap, anything apart from those items and she would have an episode.
She maintained a good weight once on the rolls, but unfortunately due to the epilepsy drugs she was on, had an insatiable hunger.
There is a canine pancreatitis group on facebook, when the vets ran out of low fat food suggestions - that group was amazing.