That's why I read xyphax. Some people read Hugo, Voltaire, and Steinbeck...I read xyphax, f.formica, mukkapazza, Viaggiatore, formaggiamente, etc. They are the best!... (too many to list or remember right now..if you are a serious student, you look for valuable information and the willingness and patience of Job"!!♡♡♡
That way, without the "se" (=if), you lose the cause / effect relationship between the two statements. You could rely on the tone of the voice to get that back, but it's wrong in general.
There are cases though, in which your attempt could succeed. For instance, when there are no verbs in the sentence.
E.g. "Niente cucina, niente pranzo".
This way, the listener / reader does not find a verb and is forced to being more "imaginative". But they are rare cases.
In italian "unless" translates "a meno che" + subjunctive, or "a meno di " + infinitive (impersonal mode)
Thus, the literal translation should be "A meno che [io] non cucini, non mangio".
Making it sound a bit more natural / fluent, it becomes "A meno di cucinare, non mangerò".
(Future sounds generally better with this construct)
So, to answer your question in a straight-forward manner, although the core meaning is almost the same, they are just two different sentences.
"se" is a conjunction. The pronoun "sé" is the reflexive tonic form. The regular reflexive form is "si". Scroll down here for the clitic pronouns: https://www.duolingo.com/skill/it/Clitic-Pronouns-1