There are many accessories available for wagonr and it depends on your requirement and budget. But the basic accessories i prefer for a wagonr lxi is a remote security lock, look for autocop or xenos brand(they wont void warranty), decent floor mats, a good car cover preferably mga, seat covers, headlight upgrades if you are not satisfied with the road visibility, a loud horn, leather for steering wheel, alloys with good rubber, and personally i dont prefer cameras on hatch backs since they are easy to drive and instead you can go for parking sensors which are useful.
For the above acessories you can go to gp road, (starting shop in gp road when coming from ea mall) shop name is mahaveer which is economical and if budget is not a problem then you can get it done at radio warehouse who are professional and premium at their job.