I won a contest. The company is sponsoring my trip. What documents do I require for a UK Visa?

Guidance on the documents you’ll need is stated here https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/549692/Visitor_Supporting_Documents_Guide_-_English_version.pdf

You’ll need to provide proof of the sponsorship, your bank statements Should I submit bank statements when applying for a UK Visa? What do they say about me? and evidence to demonstrate your ties to India How to prove that you have significant ties with family in your home country?

Note that even with a sponsor the onus is still on you to demonstrate that you qualify. IMHO, a 2 night trip as a premise for your visit doesn’t sound like a particularly credible reason so you’ll need to ensure your application is watertight. UKVI will want to verify that your competition win is bona fide.

I'd apply without mentioning a "sponsor" to make the application stronger but rather state that "somebody else would be paying for a part of your trip" (as far as I remember there's a question to this effect in the application for a visitor visa) and detailing your win in the text field.

As for the supporting documents, I'd enclose the proof of your win and focus on proving your ties to your country, e.g. a confirmation from your university, your family situation, stuff you own...

Such a short stay would probably be inexpensive, but a bank statement with some positive balance (reasonable for the area you'll be staying in) and a sensible spending history can be helpful too and also prove your ties to your country.