You don't need to be able to swim to exercise in a swimming pool. Check out hydrotherapy or aquafit sessions. I go to both and there are many non-swimmers in there. Great form of exercise, good for the joints and helps tone the droopy bits.
Many of our food cravings are down to our tongues and the oral satisfaction we get from different textures. As your is crisps then try brushing your tongue with your toothbrush when you feel the urge, so it gets the stimulation that the crunchiness of crisps gives it and see if that helps? As you tell yourself you can't have chocolates for health reasons then repeat the same for crisps. Affirmations repeated everyday for three weeks start to lodge in the brain creating automatic thoughts. Stick it on your food cupboard door to remind you.
What hobbies do you have? Do you do crafts, or something to keep you occupied? Do some volunteering, take up some study.
Thanks for the compliments