I started preparing for HSK 3 and thought I review the grammar for HSK 2 (http://hummedia.manchester.ac.uk/schools/salc/centres/confucius/hsk/grammarlists/hsk-2-grammar-points-list.pdf). In section 8, it explains the usages of 的, most of which are clear. The one I don't understand is this:
One of my guess is that 吃的 is a noun describing something that was eaten. Although, in that case the sentence would mean: I bought something that was eaten, which sounds weird :)
Having read through some of the answers here, I found that in the 是。。。的 construct, the 是 can sometimes be omitted. So the "complete" sentence would be 我是买了一些吃的。 In this case, though, 吃 would have to be a noun and I couldn't find that in the dictionary. Of course, the meaning of that would be obvious but still, I was expecting to see it defined as a noun: http://dictionary.pinpinchinese.com/definitions/s/%E5%90%83-chi
Is 的 here only to emphasise the whole sentence?