If the train you are traveling in does not provide pantry service or if you want to pick up a good restaurant for you dinner or lunch before departure,one can try the following food outlets with my opinion.
1.Refresh fast food-In the station premises exactly in front of pf five and six.Approximate cost is rs 80-100/per person.No sitting arrangements.(Recommended)
2.McDonalds is situated just outside the station.Exit point near pf 1 and just cross the road.(Okay for fast food)
3.Pizza...
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hut is just 2minutes ahead of the McDonalds.Keep walking straight ahead,you will see the Pizza hut sign board.(Big waste of money)
4.Shalimar family restaurant-AC as well as non-AC.Around 2km from CST.Good for non-veg fans.Famous in Mumbai.Catch a cab and ask the cab wala to drop you to Shalimar restaurant,Mohummad Ali road.Taxi Will cost you rs 20-25.Approximate cost is rs 600 for two.(Option only if you have more than 3 hours for departure or else risky)(Good)
5.Gulshan-e-Iran-Famous mughalai cuisine.Same way to Shalimar but before Shalimar.15 minutes walking distance from CST if no luggage.Mostly crowded, so waiting for 10-15 minutes.Cost is rs 300 for two.Same warning as for Shalimar(Best for family and non-veg lovers)
6.Delhi Darbar-Opposite to Shalimar.Famous for its Biriyani.Cost approximate 700 for two.(Recommended for biriyani lovers)
7.Many vegetarian restaurants just outside CST also.Approximate cost is rs 250 for two.