First, I'll say it how a German would say it:
"In einem Café würde ich ein Sandwich und einen Kakao bestellen. Kakao ist mein Lieblingsgetränk. Jedoch gehe ich selten in ein Café, weil es zu teuer ist."
Now my comment:
As in English, you use an indefinite article when dealing with objects you don't know already or you are speaking about in general.
You are generally speaking about what you WOULD order at A café.
As you see, in German there's an equivalent word for "would".
"I would..." = "Ich würde..."
e.g.
"I would do that." = "Ich würde das tun."
I split up the first sentence due to style. Otherwise "Kakao" has no reference to the act of ordering.