Cent.
And shift the decimal point six places so that it matches regular currencies. No regular currency is divisible to eight places. We talk about thousands or millions or billions of dollars or francs or euros, not megadollars or petafrancs. Millibits or microbits might work for geeks but not for average people.
The problem here is: You cannot produce more Bitcoins to cause inflation if they deflate to much (I guess thats what is done with 'regular' money).
What would you do if in a couple of years 1 BTC is worth $5000? You would have to pay $50 for your Coffee because there is no smaller value.
If 1 BTC = $5000, I assume you are talking about the current BTC worth roughly $20 currently increasing in value by a factor of 250x. That doesn't take into account the shift of six decimal places I mentioned. In such a case, a $2 cup of coffee would cost .0004 old BTC or 400.00 new BTC .
If you are talking about an increase in value of 250,000,000x, I think that is unreal! But if it did happen, maybe with the use of BTCs as a pan-Galactic currency, then it wouldn't be too hard to shift the decimal point another six or ten places as needed.