The following are some of the retailers located just outside Gloucester Road tube station (the one's marked (*) are a little further away from the station). 

SUPERMARKETS

• Waitrose [Inside Gloucester Arcade]
• Tesco Express

CAFÉS (HOT DRINKS, SANDWICHES, WRAPS, PASTRIES, SALAD)

• Pret A Manger
• Starbucks

• The Patisserie

FAST FOOD

• Burger King
• KFC

RESTAURANTS

• Byron (Burgers)
• Nandos (Peri Peri)
• Garfunkel's (British) [Inside Gloucester Road Arcade]
• Ask (Italian) [Inside Gloucester Road Arcade]
• Memories of India(*) (Indian) [A good curry and usual post seminar spot for the London algebraists]
• MK Bar and Grill(*) (British and European)
• The Diner (American)

Below are a list of food retailers located within the Imperial College South Kensington campus.

• Maths Common Room [Huxely building, level 5]
• Junior Common Room [Sherfield building, level 2]
• Senior Common Room [Sherfield building, level 2]
• The Library Café (Latest opening hours, baked potatoes)
• Physics Common Room (Serves the cheapest coffee in South Kensington) [Blackett building, level 8]

For more food retailers and further details on the above, see here. 

The following are some of the retailers located outside South Kensington tube station. 

CAFÉS (HOT DRINKS, SANDWICHES, WRAPS, PASTRIES, SALAD)

• Pret A Manger
• Starbucks
• Le Pain Quotidien
• La Patisserie da Reves

RESTAURANTS

• Little Japan (Japanese)
• Chopstix (Chinese)
• Billy's (Steak house)
• Wasabi (Japanese)
• Carluccio's (Italian)
• Casa Brindisa (Spanish)
• Comptoir Libanais (Lebanese)
• Khan's of Kensington (Indian)
• Rocca (Italian) [A very affordable Italian selling a range of tasty dishes]
• Franco Manco (Pizza restaurant) [Specialises in sourdough bases]
• Oriental Canteen (Chinese)
• Macellaio RC (Italian) [With an in-house butchery counter specialising in Italian beef cuts]

TAKEAWAYS

• Bosphorus Kebabs