I know katakana can be used for loanwords, onomatopoeia, strange plants, animals, for emphasis, and more. However, I don't understand why ゴミ箱 is written in katakana. Can anyone shed some light on the logic/any relevant etymology?
According to the web (e.g. this), using katakana is a way of clarifying word borders. That is, ゴミ was used for ease of reading.
The linked column and some other web pages mention that ゴミ looks more pejorative than ごみ, with which I don't really agree. But using クズ looks to me more despising somehow than くず (this is subjective visual impression).
Food names are often written in katakana, most probably for the same reason (e.g. ワカメ instead of わかめ).
The word ゴミ is indeed quite likely to be written in katakana. Come to think of it, though I don't have quantitative data, this word does have a short word form, high-frequency use, and no stable kanji spelling, all constitute factors for katakana.
The modern Japanese reading mode presupposes the mixed kanji-kana writing without spacing between words. The lack of spacing makes punctuation and script boundaries important clues in visual parsing. The longer same script (kanji-kanji, hiragana-hiragana...) continues, the more you are prone to misparse. At first sight, ごみ might be not look a common sequence, but it sometimes appears in the middle of other words: すごみ (凄み), なごみ (和み), ひとごみ (人混み), いきごみ (意気込み) etc., and ご- is also an honorific prefix. So, when ごみ is used in the middle of a run of hiragana, it might not stand out immediately to your eyes.
For example, if you first see a string 大変なごみ、それから油汚れ, it is pretty probable that you parse it like 大変 "very" - なごみ "heartwarming" - それから "moreover" - before noticing something is wrong. Keep writing ゴミ in katakana would decrease the chance of confusion in this case, but on the other hand it may be clearer in hiragana when adjacent with loanwords, such as ごみステーション.
If you look at a dictionary entry for ゴミ箱, you can see that the most common candidate for writing it all in kanji is 塵箱. 塵 is an obscure character—it's not in the set of characters taught in Japanese grade school and it's covered in the second-hardest level of the Kanji Kentei, so it wouldn't be reasonable to expect an average Japanese-literate adult to know how to read it in this day and age. As a result, ゴミ is usually written in katakana as a stand-in. This is also common in names of e.g. plants and animals, which often have obscure traditional orthography that most people wouldn't easily recognize now.