Hi Pei Yung!
Please see my suggestions and explanations below.
(1) Being a pilot is very difficult. You have to react properly in real time if an emergency happens.
(2) By the food he chooses to eat, I would guess that he is on a tight budget at the end of every month. ("Chooses" is the correct conjugation here for "he". "I can infer" is correct, but sounds very formal. We are more likely to say "I would guess". "On a tight budget" is the correct form, not "in a tight budget". )
(3) Please guard these genuine pearl necklaces in case of thieves. If you lose them, you are toast.
(4) After coming back from Japan, I am still figuring out how much the trip cost.
(5) Due to upcoming department store anniversary sales, many of my colleagues plan to buy facial products for big discounts. ("Appealing discount" doesn't sound natural. Also "discount" needs to be plural, and "for big discounts" is more natural than "with".)
(6) The warming of the globe induces glacier melts. ("Warming" is more correct than "warmth" here. Another option for this sentence is to say "Global warming induces glacier melts.)
Great job! Please let me know if you have any questions.