咩嘢 and 乜嘢, in fact no difference, you can use either one.
啲, this word is quite tricky. Sometimes no difference to use it or not in a sentence, like yours. But sometimes you cannot skip it, e.g. 呢啲咩嘢嚟㗎？ if you skip 啲 in this phrase, then it cannot become a normal phrase.