Being self-sufficient isn't about hoarding food and supplies waiting for doomsday or the world to end. It is about being able to take care of yourself and your family long term by setting yourself up to feed and provide for yourself and your family from what you produce yourself.
You can also interpret it as going off-grid with power and water backup, so you do not have to care about central services' availability.
Neither is being self-sufficient about going remote or being 100% independent.
It is not a must for you to figure out how to produce absolutely everything that you use. The modern idea of self-sufficiency is also about protecting the environment as it is about freedom and control. You can emphasize something that you like producing or doing and trade for things that other people are growing.
It is okay to trade foods, skills, and by-products with other community members.
I know a couple who live in a Costa Rica community with farmers who keep bees but do not use the bee's wax. So, they have asked if he could have it to make soaps and candles that they produce for their use and share with the farmers.
Think about a small aquaponics system, about only 3 feet wide by 2 feet deep and 4 feet tall, that can keep a dozen fish and grow several heads of lettuce at a time. It is unlikely to live off fish and salad, but this shows that you don't need a massive piece of land or significant knowledge to get started at self-sufficient.
You can research different ideas on growing vegetables, building orchards, raising livestock, or even visiting other farms to understand different systems.
It is relatively simple to get started at this no matter where you're living and even explore these ideas. It is a learning curve. Growing simple foodstuff in enough volume to put dinner on the table, you don't have to be a seasoned or professional farmer. All gardeners know that.
You can take this self-sufficiency idea and journey as far as you'd like. The point is that you don't require a lot of acreage for this as little as an acre is ample, including space for your house. If you would like to keep livestock, more space is necessary but not much more.