"There are a few super markets but i would rather bring my own food along because i might change destination or end up hitchhiking somewhere else entirely if i feel like it/if i meet an awesome person. I also want to train my body and feel the victory as i set up tent after 20 km of bushwalking !"
That's an enormous volume of food to carry, in addition of course to being an enormous weight of food. The only time I've had direct experience at someone doing something like that involved a two (full) pack system, similar to how the old gold miners in Alaska used to haul in their loads: the guy would hike one pack a few days towards his destination, hang it somewhere to keep it from animals and then hike back with minimal stuff to pick up and hike his second pack up, back and forth, so that by the time he "got there" he had hiked three times as far as he actually got. But his goal wasn't to hike a ton of miles, but rather to just spend maximal time on the trail, away from civilization.
For normal people and normal situations, I suggest that the best response to what you're trying to do is "do something else". I consider a week of food on my back to be a big load; the most I've ever carried is maybe 9 days of food, and once starting with an 8-day carry I pulled a muscle in my back dealing with the load which made my trail life unhappy for a while.
Part of the problem is that there's a sort of vicious circle that sets in where, because you have so much food weight you can't hike very many miles per day, and since you can't hike many miles per day, you need that much more food to hike the same distance. If you were 10 feet tall and proportionately strong it would of course be different, but for a typical human being --- please reconsider your plans. You're not going to "train your body", you're going to break it down, or more practically, you're going to quit your trip.
When you say "there are a few supermarkets" and that hitchhiking is an option, then keep your flexibility, but just plan on once a week or so hitchhiking or even just walking off-trail to get to place you can resupply.
If you've not done much long distance hiking before --- and thus don't have direct experience at how much food weight you can happily carry --- I would suggest that you set 10 days worth as your upper limit, but then definitely practice with your full load a time or two before setting off. Really, 10 days should be an upper limit I think if you HAVE done it before, and something lower than that if you have not. That's said, of course, not knowing anything about you.
I realize that I'm not replying to the question that you asked, and such input might be just unwelcome. I *don't* mean this in a patronizing way or anything (!), just a sense that you might be in for some pain and unhappiness if you don't adjust your plans.
And if I turn out to be wrong, please do follow-up later with details of your experience!