In my opinion, if you want to fish in Kanyakumari you might have to dedicate one evening (4 pm till 7 pm) for fishing. I was there this past July and landed a 13 pound barramundi and my friend landed a 26 pound GT. But this was about 7 km from kanyakumari, which is not far at all in my opinion. Don't even bother about taking your fishing gear within in the town. I did that last time and had a million people behind me. For Kanyakumari you definitely need heavy gear, a reel loaded with at least 30 pond mono main line to tackle mean GTs from big boulders.
If you are not planning on bringing bigger rods, at least bring a heavy reel and you can buy a heavy glass rod here for about Rs 2,000 that you don't have to worry about taking it back home. I also suggest you to bring a gaff hook, if you are planning to fish Kanyakumari, and you can tie it to a 6' metal or wooden stick and use it here. I don't think I need to say more on gaffing as I've got a lot to learn on gaffing from the Aussies :)