I'm not 100% sure on all the colonies, such as the African ones, but I can definitely say that India had to be one of, if not the most important colony Britain had. There's a reason it was called the "crown jewel" of the British Empire (other than literally being a part of the crown jewels of the empire) as it was hugely important to the British.

I wish I could find the image that showed the before/after of the GDP India had before/after the British Raj but the gap is huge. You can look at Naoroji as the father of the "drain theory" .

India was the most populous colony, which provided a surplus of labor for the empire, as well as a base to "tax" the colonies for the administration fees of running it. India also provided a lot of goods for England, such as cotton (India being a major reason why the empire didn't support the confederacy during the war) and tea, sugar cane, and textiles. Raw materials like gold, jewels (like the koh-i-noor) and other minerals were in abundance for them to take. Industry and infrastructure was also put into place by the British, using it heavily to their advantage.

India also provided a good position for Britain to have base in Asia. It's position as a peninsula was good for naval bases, and the proximity to China made it a good for trade for the empire as well. India, if I'm not mistaken, provided the most amount of Non-UK soldiers to fight in both the world wars. Lots of casualties in those wars too.

When WWII broke out, India was a good base for Britain in the Pacific, and there were legitimate fears that the Japanese were going to break through and move into India.

I'm sure there were other colonies (like Egypt) that the English used as a "bread basket" of sorts, but I doubt there were any that were on the scale of India.