1. クリームサンドビスケット: This is the name of the product coming from foreign words (Cream sand biscuits)
This picture shows the case of an おいしい biscuit that I bought from a supermarket called M2M near school. From the case we can see three biscuits and the katakana word ビスコ, which reads as bisuko, that explicitly tells us that this katakana word stands for biscuit in English. Below that, we see that there is a katakana phrase クリームサンドビスケット. Again analyzing from its pronunciation, which is kuri-musando bisuketto, we can easily know it means cream sand biscuit.
Note that the katakana forms of biscuit are different in this example (ビスコ vs ビスケット). This is something very "Japanese style". When I was watching a Japanese comic 名探偵コナン (detective Conan), I noticed that Japanese people tend to cut some syllables and make longer Japanese words shorter. For example, if we directly convert word processor in English to katakana, it would be ワードプロセッサ. But in our text book, the translation is ワープロ. Obviously some syllables of the direct katakana translation is cut in some way. Here we can see that the direct translation ビスケット (bisuketto) is shorten to ビスコ (bisuko) (note the ケ is converted to コ). In this case, the producer of this product makes the product name shorter, which means it will be much more easily for the general public to remember it, resulting in a positive feedback of the brand. This is a special case of Japanese.
Surprisingly I found there is no original word (in hiragana or kanji) that corresponds to biscuit. Look at the food culture of Japan, we can conclude that Japanese people directly made a word of hiragana from English word "biscuit", because there was no similar format of such food in Japan before (note that わがし 和菓子 is not like biscuit). This is the same for クリームサンドビスケット. Japan did not have things like cream sand biscuit before 明治維新(めいじいしん), durin which basically Japan learnt technology and science from western world. So the usage of this katakana is pretty clear here: to write foreign names and foreign words (外来語 （がいらいご)).
More surprisingly, when I searched internet with ビスコ, I found that this product has a very long history -- it has a history over 80 years. This product is produced by 江崎グリコ, which is a very famous food company in Japan (note that world-renown snack Pocky ポッキー is also produced by this company).
Check this out for more info: http://ja.wikipedia.org/wiki/%E3%83%93%E3%82%B9%E3%82%B3_(%E8%8F%93%E5%AD%90.
2. バ キッ: This is a clip from a comic called 「進撃の巨人」. The katakana here shows the sounds of the fighting between two titans.
I found this page in a very popular comic that I recently read called 進撃の巨人 (しんげきのきょじん). This story is about fighting between human and 巨人 (titans). In the comic, some people can become titans with their will freely. The above clip is about two titans (both was human) fighting each other in a battle. The katakana shown here is バ キッ. From its sound, which is bake(short stop), we can see that it is kind of imitation of a sound. From the picture, we see the scene is that two titan are fighting with each other, and the arm of one titan is broken during the fight. The katakana here wants to imitate the sound of serious bone breaking. Note that there is a stop (ッ) at the end of the sound. This is not normal in normal Japanese writing as well as reading. The author uses ッ here to show that the sound is short and quick. He might also want to tell the reader that the actions of fighting between these two titans are very quick and forceful. He may also want to show that the breaking of bones of one titan is so fierce that the sound of the process is extremely short.
Obviously the use of katakana here is for sounds. We can also see that with the "unofficial" use of ッ, the author of the comic effectively gives the reader a clear image that the fight between two titan is very quick and fierce. The special use of katakana helps us to understand what is going on more clearly.
I also note that such use of ッ is pretty usual in the comic of Japan when the author wants to show the action or the sound of characters. From my observation, during most case which uses ッ, the author wants to show that the duration of the action is very short or fierce.
3. プチ Here プチ is the Japanese way of writing a French name--Petit.
This photo is taken from a Japanese newspaper that I brought away from the plane when I flew back to United States. The プチ here is the name of a virtual character. Her name is Petit (this is a French name). In order to satisfy reader's need of reading, the editor changed Petit with Japanese pronunciation, which is puchi. Because this is a foreign word, the editor used katakana to write it out.
Such usage of katakana obviously makes it easier for non-Japanese speakers to understand things much better. If this word was written in hiragana, we might think that プチ refers to something in real world. I originally thought this word refers to ask and answer, which is the meaning of the Kanji beside プチ. But with katakana, I knew プチ refers to something non-Japanese, which is the person's name in this case. Examples like this case are seen everywhere in Japan. For instance, 烏龍 ウーロン (oolong tea) is from China. キムチ (kimuchi, a Korean food) is from Korea. These use of katakana can largely help both Japanese and foreigners to understand things more easily and faster.
