Here are some tips to follow before international travel and then I will answer your concerns.
1. Make sure to plan to reach airport 3 hours ahead of flight time. Usually airport road traffic in India is very high so keep 2-3 hours buffer in your travel plan. Some people prefer to book hotel to airport before traveling day.
2. Make checklist of documents to carry and items to carry. You are not supposed to carry anything which has seeds in it. Prohibited or restricted items may include meats, fresh fruits and vegetables, plants, seeds, soil and products made from animal or plant materials. Please visit traveling country policies before packing.
Now answers to your questions -
1. Rules to follow in Indian and Foreign airport
a. Most important do not panic at any check point if they ask you any question. Co-operate and you are good.
b. Always carry your passport in your handbag or in pockets. All the places you will be asked about it.
c. At the entrance of Indian Airport there will be security people who will check your printed air ticket and passport to allow go inside. Enough vendors are present outside in waiting area for food and drinks. Plan to bring cash or if possible water and food. Because at airport everything is expensive than outside.
d. Once inside terminal walk to your flight service kiosk or desk. Show them ticket and they will give you boarding pass. Boarding pass is nothing but flight ticket. Flights don't allow 62" linear dimension bags inside plane cabin with you so you have to check in them at the desk. Most of international long distance flights allows 2 23kg check in bags free. They tag with destination airport and you will give you small tag for cabin bags.
e. Now carry your cabin bags ( Usually allowed 2 , one with 7kg limit and another small personal item like laptop bag) and walk to security checkpoint. Place you have board plane is called gate. So before security it will be written gate numbers. Make sure you are going through right security check.
f. Remove belt, shoes and small personal items in tray. Remove laptop in separate tray. Put everything in scanning belt and stand in queue for body scan. Just follow other people and you will know it.
g. Get your stuff from other side of scan. Don't carry any liquid (>100ml) in cabin bag. Empty bottles are ok to carry. Now check signs and walk to your gate. Wait for Airline people to start boarding. In plane follow seat number written in boarding pass and take seat.
h. I advise to carry most important items like travel papers and original transcripts in cabin so you don't have to worry if your luggage to reach in destination on time.
I. At destination follow signs of luggage and wait near the carousel ( rotating belt ). Once your flight number flashes in screen , your luggage will come. Walk to ground transportation signs for your pick up or taxi.
j. Not much difference in foreign and Indian airports. Only for domestic travel you don't need to carry passport always. You can get any local govt. identification like driving license and show as proof of identity.
2. Basic rules followed in the foreign countries-
Don't rush for things, Be calm and polite. If you don't understand then contact your airline helpdesk or airport airline kiosk. Other rules are similar to follow as question 1. Speak in English as it is universal to understand.
3. Yes. Passport needed to be carried everywhere along with you for international travel.
You can purchase food once you do security check and take it inside plane too. All the best.
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