The first time I traveled internationally with high-end gear, I went through the trouble of downloading and filling out CBP Form 4457, the DHS form "Certificate of Registration for Personal Effects Taken Abroad." The idea is you fill out the form with gear and serial numbers, and a CBP (customs and border protection) official inspects your stuff and signs the form before you leave the country. The problem was there isn't anyone to sign it in a convenient location - it has to be signed by a CBP officer, and they are all in the entry areas (where you can't easily get unless you're actually entering through customs).
So, just bring copies of the invoices/receipts for the items (including your computer, if you bring one). Honestly, that's just a precaution, I have never been asked to provide documentation by Customs abroad or returning to the USA.
Definitely insure your gear, and read the policy to make sure you're covered for any type of loss and that the coverage is in force worldwide. Personally, I have mine insured with State Farm, but you exclude them (why?). Usually, coverage for personal gear (as opposed to gear used for business) is best obtained from the insurer who wrote your homeowners or renters policy, either as a rider on the main policy or as a separate policy. I pay a little over $7/year per $1K of coverage.
A related question - how are you planning on carrying your gear? Are you flying internally within India? Depending on the distance and the type of plane, a large bag may not fit for carry-on. A 5DII with 24-105, 70-200/4 and 50/1.4 doesn't take up much room, so you should be just fine. I tend to carry a lot more gear on longer trips - a fully loaded Lowepro Flipside 400 AW. I put that entire backpack into a Pelican Storm im2500 hard case, just in case I'm forced to check it.
Have a great trip!