Reduction occurs for homorganic consonants for casual, rapid speech. The degree of reduction depends on the context and the person. Example: I want to buy X. I want to [aɪwɑnttoʊ] [tt] is homorganic so [tt] > [t] I wanta [aɪwɑntə] [nt] is homorganic so [nt] > [n] I wanna [aɪwɑnə] Your question: and a I want a sandwich and a beer. [nt] > [n]; [nd] > [n]; [nd] > [n] I wanna sanwich anna beer. [aɪwɑnəsænwɪt͡ʃænəbiɹ]

I'm Australian and I agree with Alan: /ændə/ To my ear, most British people would pronounce it this way too.

Yeah, I would pronounce the 'd.' But two things: the two words can be pronounced as if a single word (an'da); and the two 'a's could be pronounced differently. When I first looked at it, I pronounced it 'ændə.' So like the 'and' in 'hand' with a quick 'duh" at the end. Note that I'm speaking as an American.

Here's a useful video about reduction of "and" in various contexts. https://rachelsenglish.com/english-pronunciation-pronounce-word/