First of all for now, 30 cents worth of BTC was enough for me to get confirmation approximately in 10 minutes. Also, such things as LN are designed to simplify such "coffee transactions". And this solution becomes pretty popular.
The other question is that why should you pay those $2-3 in BTC while there is a chance that tomorrow it could become a $4 worth of BTC? At this point it seems much easier to pay in cash.