Hello,

You need only one admit card for the examination. But for the safety purposes students carry two to three copies , if one is misplaced somewhere then you can use the others as you will be not allowed to sit in the examination hall without admit card so special care is taken.

For the dress code you can go through the guidelines given on the 2nd or 3rd page of your admit card. However wearing t-shirts and trouser will be no issue to sit in the examination hall. It is advisory only not to wear clothes having big buttons or the shoes with thick soles. For more information you can go through the article below:
https://medicine.careers360.com/hi/articles/neet-dress-code

Thank You!