Once you come back to India, you can go through two channels-green or red. If you don't have an item that is likely to attract duty, you can go through the green channel, otherwise you will have to go via the red channel. At the latter, you will be given two declaration forms, one for the custom goods (you may need to pay customs duty for some items) and the other for foreign currency.
You need to mention if you have foreign currency notes worth more than $5,000 or an equivalent amount. You will also have to declare if you have more than $10,000 as foreign exchange, including currency, TC or prepaid cards.
Don't think that buying items at duty-free shops means you can escape the customs duty. This is only exempt for goods worth Rs 25,000. You will have to pay duty on the goods that cost more than this amount. You cannot combine the exemption limit for two people.
For instance, if you are travelling with your spouse and have bought a camera worth Rs 40,000, it will have to be declared in the name of one person and you will have to pay duty on the remaining Rs 15,000. The customs duty is 35%, along with an education cess of 3%, which brings the total tax to 36.05%.
However, you will not have to declare anything if you only have personal items, one laptop and foreign currency that is within limits.
Your responsibility is not over once you walk out of the airport. You need to dispose of the unused foreign exchange because you are not allowed to keep more than $2,000 as foreign currency notes.
Any cash in excess of this amount needs to be surrendered to a bank within 90 days. If it is in the form of travellers' cheques, you can return it within 180 days of returning from abroad. However, you can hold any amount of foreign coins.