i buy in bulk, especially lentils and beans (dried, so cookyourself) i buy big bags of frozen foods like peas and corn etc, and also i shop when fruit goes on sale, i buy bananas and freeze them for protein smoothies, also buy protein powder from Vega… they have 20% off sale right now in canada and usa. pasta, rice is cheap as well. i shop at a wholesale store so they have huge quantities of their items big sac of potato etc… also have you thought of pitching in for groceries? you are a teenager im sure you could easily snag a job a couple days a week if u wanted to buy urself some “expensive vegan treat food” why does your dad think veganism is expensive? your litterally taking away items from your dinner plate, meat dairy etc… and relacing them with a couple simple plant based foods
I hope that you manage to get a good job. Be inventive with yourself: I was like you until my 30s when I started busking with an old recorder and selling "The Big Issue". Join the job seeking sites on Facebook, Indeed, Seek etcetera. Do everything you can to save and follow the advice of penguinnnnnnn (in answer above). You dont have to be low-income for the rest of your life…you just have to be smart.