For one to be able to live from farming he needs a quite large area to do that, the backyard just won't be enough. And it's hard work. But if any Bernd wants to plant crops now it is the time.
Don't forget pests and animals that might reap the fruits of your work. Viruses, bacteria, fungi, insects, snails can all harm your crops. Some birds too, but birds can help too with feeding on some pests.
As for chief source of carbs probably potato is the best since, wheat, rice and corn cannot be produced in any useful quantity in the backyard. For potato I would try out picrel. It might work. Also plant beans, when dried it will store long.
Besides the usual veggies other plant based food source can be cultivated on purpose, which some would consider just weed, like nettle and dandelion, they need less care. Also nettle can be used to make cordage if need be, and self reliance is the topic.
As for animals. If you have goats and chickens, you have three source of whole protein, meat, milk and eggs. While goat leather I think not the most famous and best but that can be used too, also tendons. However I'm not sure the legal background, in some neighbourhoods keeping livestock might be verboten, not to mention butchering, I'm sure EU has some regulations. Btw goats are very hardy and undemanding, but they eat everything, so keep them away from the crops.