Bring your own mat. Over the month of a teacher training you spend more time on the mat than in your bed, so make sure its a good one. I think the key to a decent mat is one that is grippy so you don’t get slippy. There are some really great recycled rubber ones around at the moment. Check out Manduka.com
Think about the environment you will be in. Hot or cold. Windy or rainy. When I did my first teacher training it was in a very hot climate and it played a huge role in my ability to practice and my energy level. If I could repeat it again I would have brought completely
breathable cotton clothing. When you choose yoga clothes you need to be mindful that a lot of Teachers on a TTC expect to be able to analyse and asses what is going on in your body, so they want to be able to see the muscles. So unfortunately loose and baggy sometimes isn’t an option.Often you read online that you can’t wear tight clothing in India for asana practice. Well I think as long as you are not wearing your undies and your intention is right then there won’t be a problem.
You really don’t need much. You can buy everything here. Bring your prized lotions and potions but other than that most is available. I will say though if you can’t bear mosquitos then get a good repellant from your home country as most ones I’ve used in India seem to be pretty immune.There is a great array of health products from Ayurvedic to weird and wacky. There is a cream for everything!