Containers have to become a lot more expensive to have that effect. Per unit costs are still a fraction of total costs, so I wouldn't worry to much about that.

If containers become more expensive only high profit margin products will be able to afford it.

I have the impression that the highest profit margins typically fall on non essentials

...and then what would happen to the price of essentials vs non-essentials...take this one step further and you've found the answer to your question.

Is it that easy? It seems, that only works if people can pay for the essentials. For example, look at the grain prices that sparked the protests of the arabian spring. People could everywhere not afford their bread anymore while Saudi Arabia bought the grain at ultra high prices.

Yes, it's that easy. And prices of commodity food staples only cause unrest in very poor nations where food inputs constitute a large % of their income.

Wheat costs about $200/ton and peaked around $450/ton during the arab spring period. A ton of wheat (with a few supplements) is enough to for 500g/day for 5 people for a year if half your calories come from wheat. Even at $500/ton, that's about $100/yr/person for the wheat itself. Wholesale raw foods are quite cheap from the perspective of someone in a rich nation. Can be quite expensive for the very poor. The solution is to help people in poor nations industrialize so that they are less poor.

I don't know, right now the item that has been most affected in the UK is garden furniture. That hardly falls in the essential category.