@reallybloodytired first of all, it will be fine, he is 7 months, not 7 years old, we can fix this shaky start.
First step, you have to - as many have said - to stop giving puffy snacks and other baby junk food because they are engineered to be addictive. Melty puff are no different than Cheetos, you can't stop eating them and they have the same ingredients, texture, and if you keep giving them, you risk that you baby boy will only eat processed foods.
You also need to break this habit of giving food in pool, car or wherever until real food habits are rooted. IF you start giving junk food whenever baby is unhappy you are creating a second ( and bigger) problem.
Now, easy to tell you to remove crisps, but what next? 
In a recent discussion, I give a mother some ideas on what and how to prepare for a baby here. www.mumsnet.com/Talk/breast_and_bottle_feeding/4292911-Weaning-5-months
To you, I add that you need to understand how sucking, chewing and swallowing work form a mechanistic point of you. A baby needs to learn to chew to produce saliva that will lubricate the food. otherwise there is the reflex to spit it out. So first foods need to be wet until baby has learned that. Imagine yourself having to swallow a big spoonful of dense mashed potato with no sauce and without doing any movement with your jaw, just told to swallow. IT gets stuck.
Ultra processed baby food such as melty puff or rusk dissolve in the mouth and the ultra proceeding will produce this sweet feeling in the mouth.
So, this is how you are going to do it. Take a 48 hours break, during which increase the milk to compensate for lack of food. During this time, go shopping with him, in the fresh aisle or grocers shops or market if there is one. Do NOT give him snack to keep him happy. Whenever you pick a fruit of vegetable, show it to him, even if you have to squat to his level, or present it to him before putting it in a bag. Select your fruit and veg and then pay and go home without visiting the baby food aisle. . Have him in your arm while you fill your sink with water and wash the fruits and vegetables , then next to you, while you peel and cut them. If you have to do it on the floor, so be it. Put newspaper under the chopping board.
You have given him high palatable food, which combines the sweetness of corn , with oil and the saltiness of veggie powders and this combination that doesn't exist in nature (sweet+fat+alt) is the key to making people go nuts (think about eating chips without salt, not the same thing) , so now as first food you need to be able to find this delicious taste.
In Italy, where my DD was born, they start with a rich broth ( cut into pieces carrots, zucchini, onion, ripe tomatoes, celery in a pot of water and let it simmer for a couple of hours, discard the veggies, put press them a bit before doing filtering the broth) put a ladle or two of broth in your smallest pot, and when it boils, add baby pasta (the dot or similar size one) and cook for the amount of time on the packet. Once it is cooked , remove a ladle of pasta/broth , put a tiny bit of real butter , parmigiano reggiano grated cheese, and you will have the combination of sweet (pasta) + fat (butter) + saltiness (cheese). Make sure it is still very liquid. When it has cooled down, fill half the spoon, with mix of pasta and broth. Don't go deep in the mouth, just pass the lips, this will create a reflex with the tongue.
In Italy, broth is the base for weaning. It is used for pasta (of course, Italy!) , but also soupy risottos, and later when babies eat shredded meat, a bit is added in the last minute to the pan to have it more sauce-y.
Fruit, think about, juicy and cold watermelon, or a ripe melon (cut in half, once you have removed the seeds, with a metal teaspoon, dig some flea from the centre , again half the spoon) or apple sauce, pear sauce, .... Ice-cream again combines fat and sweet, don't give it. You can blend the flesh of watermelon and put in a very tiny container in the freezer, until it is starting to solidify, then with a spoon, just give the tiniest taste, never overfill the spoons.
Then once these are accepted it is time to open more foods, and soups can go down better than purees. You can make them more of less thicker and again, think about that 1 cm of butter and some parmigiano reggiano .
Whenever you can, have him in your arms, resting on your hip , when you prepare the food. IF you have an oven, think about sliced pumpkin cooked in a tray with extra virgin olive oil, with a couple of garlic cloves in the corners, and a branch of rosemary. Let the pumpkin cook, until it caramelises . Again let cool. The pumpkin should break down under the pressure of the fork. Many veggies roast beautifully in the oven, zucchini, sweet potato...
Even if you don't have a table , you can have him next to you while you eat. Sit crossed legged on the floor , with him between your legs while you hold your plate. He will have his nose in your plate. He will be curious, and reach for the food, let him take a small piece not a handful Of course , this means you have to reflect on what you eat as a parent because if you are having take away or ready meals, or other processed food, you are not introducing good habits.
While you cook, have him on the floor at your feet and give him a silicone tool or a wooden spoon and an empty pot in which you have placed an apple, a fennel, even a branch of celery, put the lid back on, and you let him play with that , he will bring them to his mouth and get the taste even if only by licking it. Everyday change what you give him, hidden in the pot (a bit like a culinary treasure basket) , give him kitchen tools that are safe, and new fruits and veggies, maybe a slice of omelette one day, when he starts eating more.
When he is more accepting of his chair, have him next to you while you cook, and give him some food to copy you (everything will land on the floor, just so you know) .
Yes, far more work than opening a pack of crisps, but you can save this situation.
I hope, some of what I have typed will be of some help. Good luck 