Allied naval blockade in WW2 had only marginal . There were a number of changes compared to WW1.
Germans were prepared for a blockade, they had experience for it from WW1. Advancements in chemical industry allowed for independence from overseas imports of exotic/important raw materials like rubber or oil. Agriculture was prepared to make the country self sufficient before the war, and in addition plenty of supply could be obtained from occupied, agricultural rich countries (Poland, France).
Large investments were made into synthetic chemical products. This was a correct and conscious decision made before the war, even if it went against traditional economic considerations for maximum profit/complementing advantages in production.
Also, unlike WW1, for a large part of WW2 most of Europe was either friendly to Germany or neutral. Their own economic capacity was unhindered by own war effort needs, and the only real trade partner due to the Axis blockade of England was effectively Germany, which had the purchasing power. Rumanian oil, Turkish chromium, Hungarian bauxite and foodstuff, Finnish nickel, Swedish iron ore was available for the Germans regardless of maritime trade.
The USSR was a major supplier of strategic items, and after the conquest of much of the USSR its rich lands remained so regardless. Trading could be also pursued through neutral countries as proxies, like i.e. Spain, though this was limited during the war.
For the above reason, a naval blockade was doomed to fail - Germany was simply not isolated from the rest of the European economy as it was in WW1. Shortages in critical supplies were only felt after the Germans effectively lost the war on the battlefields in 1944, and it prompted Finland, Turkey, Rumania to cease supplies for one reason or another.
