As a midway point between ないで ‘please don’t’, and な ‘don’t!’, 関西弁（かんさいべん） uses a unique structure, なさんな. なさんな is a combination of the 尊敬語（そんけいご） (honorific speech) word なさる, and the 終助詞（しゅうじょし） (sentence ending particle) な.
なさる is a polite (slightly outdated) version of する, used to refer to the actions of others (never oneself). なさる conjugates with the 連用形（れんようけい） (conjunctive form) of verbs, meaning that なさんな will also conjugate in the same way.
It's okay if you don't eat everything, don't force yourself to eat it.
It seems like he regrets what he did, so don't yell at him.
Please don't hesitate.
We will provide you with lunch, so please don't bring your own.
Fun-fact - There are many cases in Japanese where the terminal る (of verbs) will be omitted, due to the shortening of sounds within speech. While this is technically slang, it is a common feature worth memorizing. When る is omitted, it will almost always be replaced by the ん sound, as seen with なさんな. A few more examples are as follows:
するな - Will become すんな, ‘don’t do!’
踊（おど）るな - Will become 踊（おど）んな, ‘don’t dance!’
走（はし）る - Will become 走（はし）んな, ‘don’t run!’