"May I have a coffee and sliced bread, please?"
Translation:Puis-je avoir un café et une tartine, s'il te plaît ?
The "question+infinitive" structure is never connected (although it is pronounced as though they are connected in fast speech). When you put s'il vous plaît in the middle of the sentence like that, it just makes the sentence sound a little stilted and weird. I think it sounds weird because it splits the auxiliary verb (puis) and the infinitive -- I would never say that.