Honestly, BTC is hard to be used comfortably because now it is easily volatile and not stable. Its price is fluctuating all of time. Furthermore, it still has more the speculation. But if BTC can fix all of its shortcoming, it would be regulated and popular in any transaction in the world. Since btc has more advantages by its technology. At that moment, people would feel comfortable using BTC as a real currency.
If you buy it at low levels, you won't care as much about the fluctuations. If you want to use it for small purchases as the OP said (which I think is extremely impractical) then you wouldn't really care much about those small differences in price.
Bitcoin is much better used as a store of wealth to contain money rather than as something to buy lunch with. It's more useful to have large transactions and use the money you take from bitcoin to buy something useful or invest in something else, like mining mentioned above.
Interestingly most people either spend less than 10% or most. But there are only 14 votes. Instead of spamming with nonsense ideas, people should contribute to the OP's study and vote.