The basic meaning of もの is just *thing* rather than *something*. なにか/なんか adds the nuance of "seeking" (i.e., you are trying to find/identify something that fits the criteria, although you don't know what "it" is exactly).

- 飲むもの things to drink, beverage
- 何か飲むもの something to drink
- 食べたいもの things you want to eat
- 何か食べたいもの something you want to eat
- 怖いもの a/the scary being (may be already identified)
- 何か怖いもの something scary (unidentified)

In your examples, 何か is not strictly necessary, but it's often desirable. On the other hand, you cannot use 何か when you already know what the もの refers to:

- 持っているものを見せなさい。  
  Shoe me the thing you have.
- 私は食べたいものを食べます。  
  I eat (any)thing I want to eat.