Japanese snacks are all good and affordable, so they are always are piled up ion my shelf. Japanese snacks are all good and affordable, so they are always piled up on my shelf.

I don't think what you wrote is wrong, but this order is much more natural.

Japanese snacks are all good and affordable, so they are always are piled up in my shelf. Japanese snacks are all good and affordable, so they are always piled up in my shelf.

分かるーIt's the same thing for me!

Japanese snacks are all good and affordable, so they always are piled up ion my shelf. Japanese snacks are all good and affordable, so they always are piled up on my shelf.

Your shelf is an open place, so on.

ALSO POSSIBLE: Japanese snacks are all good and affordable, sobut they always are piled up in my shelf. ALSO POSSIBLE: Japanese snacks are all good and affordable, but they always pile up in my shelf.

Salty snacks and chocolates are very popular in Japan. Salty snacks and chocolates are very popular in Japan.

I prefer salty ones though. I prefer salty ones though.

I prefer salty ones though. I prefer salty ones though.

I prefer salty ones though. I prefer salty ones though.

Plural since you are referring to multiple (a type) of snacks (the salty ones)

I prefer salty ones though. I prefer salty ones though.

I prefer salty ones though. I prefer salty ones though.

You prefer many salty snacks so ones instead of one

I prefer salty ones, though. I prefer salty ones, though.

What kind of snacks are popular in your country? What kind of snacks are popular in your country?

In my country, Poha is very much eaten. It varies if you are from North or South India. In the North, here, we like poha.

Eating late-night snacks occasionally when I study English. Eating late-night snacks occasionally when I study English.

Eating late snack occasionallyMy guilty pleasure is occasionally eating late night snacks when I study English. My guilty pleasure is occasionally eating late night snacks when I study English.

Eating a late snack occasionally when I study English. Eating a late snack occasionally when I study English.

Need an indefinite article before the noun

EOccasionally eating late snack occasionallys whenever I study English. Occasionally eating late snacks whenever I study English.

Eating late snacks occasionally when I study English. Eating late snacks occasionally when I study English.

Eating late snacks occasionally when I study English. Eating late snacks occasionally when I study English.

NOTE: The plural "snacks" is better here . . .