when i traveled around the world last year (including a visit to delhi, mumbai, and goa), i posted a ridiculously detailed packing list on my blog site at http://goneliving.com/packing-list.html. you can obviously remove items you won't need (for example, DIY laundry supplies since we'll be at places that will have laundry services).
for clothing, i tried to pack a series of layers that worked well for hot/humid days, but also could be combined together in case things got really cold. the list goes through the clothing item-by-item.
i'm a HUGE fan of the eagle creek or victorinox packing cubes (see the list for details and the usual buy-me-on-amazon links). these are great for organizing your clothing, and they have the added bonus of compressing things down and making it really easy to load/unload your suitcase. and since they're in standard sizes, they also fill the interior of most suitcases without any wasted space.
and the short list of 5 items from my packing list that i couldn't live without:
1. a pair of flip-flop style sandals that you've tested, know and love. these will probably be your primary footwear. flip-flop style sandals are essential for taking on and off easily when entering and leaving temples, etc... no fussing with teva's velcro (and nobody else will wearing tevas). i recommend reef sandals.
2. sound-isolating in-ear earphones (lots of companies make these nowadays... they're small and block out screaming babies, annoying airport announcements, and all that stuff. i like the Shure headphones) and my trusty ipod.
3. pocket-sized mini tripod for my small digital camera (with velcro attachment to attach it to buildings or scaffolding when needed for that perfect long-exposure shot)
4. beach towel (i've tried using a sarong as a towel, and i much prefer a regular beach towel). note: yes, you can buy a beach towel locally, but beware of getting one with dyes that transfer onto your wet skin while you're lying down on it, as my cheap beach towels did in fiji. i have a long rant about this at http://www.goneliving.com/egypt/backpacker_product_of_the_year_the_microfiber_beach_towel.html (note that billabong appears not to make their awesome microfiber beach towel anymore)
5. everything else: laundry bag, flashlights, swiss army knife, titainum mug (light and good for those homemade cocktails), empty pillow case (handy for filling with clothes when you need an instant extra pillow), wet wipes, playing cards, ziploc bags... see the packing list for details.
i'm looking forward to going back to india this winter!