Some foods all dogs should avoid are onions, grapes/rasins/currants, chocolate(especially Dark Chocolate), avacadoes, onions, garlic, persimmons, rhubarb leaves, high amounts of any type of fish, raw eggs and meat and anything with alcohol or caffeine in it. Because Jacks are small dogs even consuming small amounts of these foods could be deadly.
You should try to avoid sweet foods such as chocolate
Any foods that have a high sugar level content or junk foods are the foods that you should avoid. Have fresh fruit and vegetables every day to keep you , or concentrated in class, work etc.
You should avoid high calorie foods because they will make you gain weight. You should avoid acidic foods because they will give you indigestion.
Fat foods
fatty foods
Avoid eating salty foods, Foods that have lots of grease, and foods that are thick.
I am not sure which foods you should aviod with colitis. I have never known anyone who actually has colitis. You should contact your local doctor to avoid with colitis
Fattening foods, sweets, and chips or junk foods...
avoid hard-to-digest foods such as nuts, corn, popcorn, and seeds
Betroot
starches
You should be tested by an allergist so you are aware of the specific foods you are allergic to. Those are the foods you should always avoid.