1. I drink a coke.
2. I drink a Coke.
3. I drink cola.
4. I drink a cola.
5. I drink a glass of coke.
6. I drink a glass of cola.
(Which expressions are correct?)
7. My favorite food is seafood, rawfish, dumplings, salad, and live octopuses. (Is this sentence grammatical? Do I have to use 'My favorite foods are.....)
8. I like soy bean paste soup.
9. I like soft beancurd soup.
10. I like boiled squids. It's great to dip pieces of boiled squids into a vinegar hot pepper paste.
(Are the sentences right?)
1 - 6 are all correct except that when you are referring to colas with the brand name Coca Cola ("Coke") be sure to use capital "C" -- the word "cola" is generic and can be used for any brand, such as Pepsi or others.
7 - Since you have named several types of food, you should use the plural (although "types of food" is better than "foods"). Also, it's "raw fish" (2 words).
8 - 10 are all correct except for the word "squids" -- usually this word is used only in its singular form, no -s attached.
There are several words in English that are used only in the singular form even if you mean plural. Here are a few examples:
squid
deer
elk
caribou
bread (for plural, you'd say "loaves of bread" or "slices of bread")
fish (I've seen "fishes" but usually as a verb or by a young child who is still straightening out his/her grammar!)
1. I drink a coke. - This sentence is grammatically correct, but it should be noted that "coke" is a common way to refer to Coca-Cola specifically. If you are referring to a generic cola or carbonated beverage, it would be more accurate to say "I drink a cola."
2. I drink a Coke. - This sentence is also correct. "Coke" is capitalized here to indicate that you are referring to the specific brand Coca-Cola.
3. I drink cola. - This sentence is correct and refers to the generic type of carbonated soft drink.
4. I drink a cola. - This sentence is grammatically correct, but it is less common to refer to a specific instance of cola using the article "a." Typically, people say "I drink cola" to refer to drinking cola in general.
5. I drink a glass of coke. - This sentence is correct, but similar to the first point, if you are referring to a generic cola, it would be more accurate to say "I drink a glass of cola."
6. I drink a glass of cola. - This sentence is grammatically correct and refers to drinking a specific amount of cola.
Regarding the other questions:
7. My favorite food is seafood, rawfish, dumplings, salad, and live octopuses. - This sentence is not grammatically correct. In this case, you should use "favorites" or "favorite foods" rather than "food" to match the plural list of items. It should be "My favorite foods are seafood, rawfish, dumplings, salad, and live octopuses."
8. I like soybean paste soup. - This sentence is grammatically correct. It expresses a preference for soybean paste soup.
9. I like soft beancurd soup. - This sentence is also grammatically correct. It indicates a preference for soft beancurd soup.
10. I like boiled squids. It's great to dip pieces of boiled squids into a vinegar hot pepper paste. - This sentence is mostly correct, but the plural form of "squid" should be used, so it should be "I like boiled squids." Additionally, "vinegar hot pepper paste" should be "vinegar and hot pepper paste."